Thermal energy storage

ABSTRACT

The invention is directed at articles and devices for thermal energy storage, and for process of storing energy using these articles and devices. The articles comprise a capsular structure  10  having one or more sealed spaces  14,  wherein the sealed spaces encapsulate one or more thermal energy storage materials  26:  wherein the capsular structure has one or more fluid passages  16  which are sufficiently large to allow a heat transfer fluid to flow through the one or more fluid passages; and when a heat transfer fluid contacts the capsular structure  10  the thermal energy storage material  26  is Isolated from the heal transfer fluid. The devices include two or more articles arranged so that a fluid, such as a heat transfer fluid, may flow through the fluid passage  16  of an article before or after flowing through a space between two of the articles.

CLAIM OF BENEFIT OF FILING DATE

The present application claims the benefit of the filing date of U.S. Provisional Application Ser. No. 61/299,565, filed Jan. 29, 2010, which is hereby incorporated by reference for al purposes.

FIELD OF THE INVENTION

The present invention relates to thermal energy storage using a thermal energy storage material and to the packaging of the thermal energy storage material to allow for both efficient heat storage and efficient heat transfer.

BACKGROUND OF THE INVENTION

Industry in general has been actively seeking a novel approach to capture and store waste heat efficiently such that it can be utilized at a more opportune time. Further, the desire to achieve energy storage in a compact space demands the development of novel materials that are capable of storing high energy content per unit weight and unit volume. Areas of potential application of breakthrough technology include transportation, solar energy, industrial manufacturing processes as well as municipal and/or commercial building heating.

Regarding the transportation industry, it is well known that internal combustion engines operate inefficiently. Sources of this inefficiency include heat lost via exhaust, cooling, radiant heat and mechanical losses from the system. It is estimated that more than 30% of the fuel energy supplied to an internal combustion engine (internal combustion engine) is lost to the environment via engine exhaust.

It is well known that during a “cold start” internal combustion engines operate at substantially lower efficiency, generate more emissions, or both, because combustion is occurring at a non-optimum temperature and the internal combustion engine needs to perform extra work against friction due to high viscosity of cold lubricant. This problem is even more important for hybrid electric vehicles in which the internal combustion engine operates intermittently thereby prolonging the cold start conditions, and/or causing a plurality of occurrences of cold start conditions during a single period of operating the vehicle. To help solve this problem, original equipment manufacturers are looking for a solution capable of efficient storage and release of waste heat. The basic idea is to recover and store waste heat during normal vehicle operation followed by controlled release of this heat at a later time thereby reducing or minimizing the duration and frequency of the cold start condition and ultimately improving internal combustion engine efficiency, reducing emissions, or both.

To be a practical solution, the energy density and the thermal power density requirements for a thermal energy storage system are extremely high. Applicants have previously filed 1) U.S. patent application Ser. No. 12/389,416 entitled “Thermal Energy Storage Materials” and filed on Feb. 20, 2009; 2) U.S. patent application Ser. No. 12/389,598 entitled “Heat Storage Devices” and filed on Feb. 20, 2009, and 3) PCT Application No. PCT/US09/67823 entitled “Heat Transfer Systems Utilizing Thermal Energy Storage Materials” and filed on Dec. 14, 2009. These previous applications are herein incorporated by reference in their entirety.

There are known heat storage devices and exhaust heat recovery devices in the prior art. However, in order to provide a long term (e.g., greater than about 6 hour) heat storage capability, they generally occupy a large volume, require pumping of a large volume of heat transfer fluid, require a relatively large pump to overcome the hydraulic resistance, and the like. Therefore, there is a need for a heat storage system which can offer an unprecedented combination of high energy density, high power density, long heat retention time, light weight, low hydraulic resistance for heat transfer fluid flow, of any combination thereof.

SUMMARY OF THE INVENTION

One aspect of the invention is an article comprising a capsular structure having one or more sealed spaces, wherein the sealed spaces encapsulate one or more thermal energy storage materials; wherein the capsular structure has one or more fluid passages which are sufficiently large to allow a heat transfer fluid to flow through the one or more fluid passages; and when a heat transfer fluid contacts the capsular structure the thermal energy storage material is isolated from the heat transfer fluid.

Another aspect of the invention is a device including a container and a plurality of the articles having a fluid passage and containing the thermal energy storage material, such as a plurality of articles described herein, wherein the plurality of articles are stacked so that the fluid passages are aligned axially.

A process related aspect of the invention is a method for removing heat from a heat storage device, such as a device described herein wherein the process includes a step of flowing a heat transfer fluid through the device. Preferably, the process includes flowing a heat transfer fluid having an initial temperature through an inlet of the device; flowing the heat transfer fluid through an axial flow path so the heat transfer fluid can be divided into e plurality of radial flow paths; flowing the heat transfer fluid through a radial flow path so that it can remove heat from the thermal energy storage material, wherein the thermal energy storage material has a temperature greater than the initial temperature of the heat transfer fluid; flowing the heat transfer fluid through a different axial flow path so that a plurality of radial flow paths can recombine; flowing the heat transfer fluid having an exit temperature through an outlet of the device; wherein the heat transfer fluid exit temperature is greater than the initial temperature of the heat transfer fluid.

Another process related aspect of the invention is a method for preparing or assembling an article including cutting an opening in a base sheet, embossing a base sheet so that it has one or more troughs, filling one or more troughs with a thermal energy storage material, cutting an opening in a cover sheet, and sealingly attaching the cover sheet at least along an outer periphery and an opening periphery to the base sheet so that an article having one or more sealed spaces containing the thermal energy storage material is formed.

Yet another aspect of the invention is a system including a heat storage device, such as a heat storage device described herein, and a heat transfer fluid, wherein the heat transfer fluid is in thermal communication with the thermal energy storage material in a sealed space (e.g., a sealed space of an article in the heat storage device).

The articles, devices, systems and processes of the present invention advantageously are capable of containing a high concentration of thermal energy storage material so that a large amount of thermal energy can be stored (e.g., having a high energy density), are capable of having a high surface area between the heat transfer fluid and the article containing the thermal energy storage material so that heat can be quickly transferred into and/or out of the thermal energy storage material (e.g., having a high power density, preferably greater than about 8 kW/L), are capable of having multiple flow paths that have similar or equal hydraulic resistance so that heat is uniformly transferred to and/or transferred from different regions; have a rotational symmetry so that they may be arranged easily; have a structure that is strong and durable; have a high heat storage density so that they can be used in applications requiring compact designs, light weight components, or both; have lower hydraulic resistance for a heat transfer fluid flow (for example, a pressure drop of less than about 1.5 kPa at a heat transfer fluid pumping rate of about 10 liters/min) so that the pumping requirements for the heat transfer fluid are reduced, or an combination thereof.

BRIEF DESCRIPTION OF THE FIGURES

The present invention is further described in the detailed description which follows, in reference to the noted plurality of drawings by way of non-limiting examples of embodiments of the present invention, in which like reference numerals represent similar parts throughout the several views of the drawings, and wherein:

FIG. 1A is a drawing of an illustrative article having one more sealed compartments and a fluid passage.

FIG. 1B is a drawing of an illustrative article having a plurality of segments each containing one or more sealed compartments. The segments are arranged so that the article has a fluid passage.

FIG. 2A is a drawing of an illustrative article having a sealed compartment and a fluid passage.

FIG. 2B is a drawing of an illustrative cover sheet having a fluid passage that may be employed in the article.

FIG. 2C is a cross-section of an illustrative article, such as the article illustrated in FIG. 2A.

FIG. 2D is cross-section of an illustrative embossed base sheet that may be employed in an article.

FIG. 3A is a side view of two illustrative adjacent segments that may be employed in an article. The segments may have an edge that generally mate.

FIG. 3B is a side view of two illustrative adjacent segments that may be employed in an article. The segments may have an edge that generally mate.

FIG. 4 is a side view of adjacent segments that mate along their edges when one of the segments is shifted so that the adjacent segments bottom surfaces of the segments are on different parallel planes.

FIG. 5A is a drawing of an illustrative embossed base sheet having a plurality of troughs that may be used in an article having a plurality of sealed compartments containing thermal energy storage material.

FIG. 5B is a drawing of an illustrative portion of the embossed sheet of FIG. 5.

FIG. 5C shows an illustrative stack of articles having corresponding fluid passages.

FIG. 6A is a drawing of an illustrative article having one or more surfaces containing a plurality of grooves extending from the opening to the outer periphery.

FIG. 6B is a drawing showing the interface between a bottom surface of a first article and the top surface of a second article when the two surfaces each have a plurality of curved grooves.

FIG. 6C is a drawing of two segments of an illustrative article.

FIG. 6D is a side view of a stack of the segments of FIG. 6.

FIG. 7 is a top view drawing of an illustrative article having a top surface that is non-circular and/or has an opening that is non-circular.

FIG. 8 shows a cross-section of an illustrative heat storage device including a stack of articles in a container.

FIG. 9 is another cross-section of an illustrative heat storage device including a stack of articles in a container.

FIG. 10 is a schematic drawing showing illustrative features of a thermal energy storage system.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In the following detailed description, the specific embodiments of the present invention are described in connection with its preferred embodiments. However, to the extent that the following description is specific to a particular embodiment or a particular use of the present techniques, it is intended to be illustrative only and merely provides a concise description of the exemplary embodiments. Accordingly, the invention is not limited to the specific embodiments described below, but rather; the invention includes all alternatives, modifications, and equivalents falling within the true scope of the appended claims.

As will be seen from the teachings herein, the present invention provides unique articles, devices, systems, and process for storing thermal energy and/or transferring stored thermal energy to a fluid. For example, the articles and devices for storing thermal energy of the present invention are more efficient at storing thermal energy, allow for transferring thermal energy more uniformly, allow for transferring thermal energy with a smaller pressure drop of the heat transfer fluid, or any combination thereof.

Various aspects of the invention are predicated on an article including a capsular structure having one or more sealed spaces (i.e., capsules) and one or more thermal energy storage materials that are encapsulated in the one or more sealed spaces of the capsular structure so that the thermal energy storage material cannot flow out of the capsular structure or otherwise be removed from the capsular structure. The capsular structure has a novel geometry that includes one or more fluid passages that are sufficiently large so that the capsular structure is capable of allowing a fluid (e.g., a heat transfer fluid) to flow through the fluid passage. The thermal energy storage materials are sufficiently encapsulated in one or more of the sealed spaces so that when the heat transfer fluid contacts the capsular structure, the thermal energy storage material is isolated from the fluid. Other aspects of the invention include novel arrangements including a plurality of the articles, novel devices including one or more of the articles, novel processes for manufacturing the article, and novel processes for using one or more of the articles. By employing the novel article, it is possible to assemble devices capable of storing a large quantity of thermal energy, capable of rapidly transferring thermal energy into or out of the thermal energy storage material, capable of being compact, capable of being light weight, capable of having a low pressure drop of a heat transfer fluid, or any combination thereof.

Capsular Structure

The capsular structure generally has a dimension in one direction (i.e., a thickness) that is smaller than the dimensions in the other directions. The capsular structure has one or more openings (i.e., fluid passages), preferably in the smaller direction of the capsular structure.

Opening/Fluid Passage

The capsular structure has one or more fluid passages. Preferably the capsular structure has one fluid passage. The one or more fluid passages may allow a fluid, such as a heat transfer fluid to flow through the article without contacting the thermal energy storage material. The fluid passage (e.g., the cross-sectional area of the fluid passage) preferably is sufficiently large so that the heat transfer fluid can flow through it with minimal loss in pressure. The fluid passage preferably is near or includes the geometric center of the capsular structure. As described hereinafter, an fluid passage that is near or includes the geometric center of the capsule may allow the article to be employed in a device that is characterized generally as a Tichelmann system.

The fluid passage may be of any cross-sectional shape that facilitates passage of fluid through the capsular structure. Without limitation, the fluid passage may have an axial direction and a cross-section of the fluid passage with a plane normal to the axial direction may be generally circular, generally polygonal, or generally oval shaped. Preferably, the fluid passage has a generally cylindrical shape. For example the fluid passage may have an axial direction and the cross-section of the fluid passage with a plane normal to the axial direction may be generally circular.

The length of the fluid passage may be any length that allows for efficient heat transfer and preferably is the thickness of the capsular structure. The size of the fluid passage is a measure of the diameter of the fluid passage (e.g., for an fluid passage having a generally cylindrical shape) or twice the shortest distance from the center of the opening to a surface of the capsular structure. The size of the fluid passage is preferably greater than about 0.1 mm, more preferably greater than about 0.5 mm, even more preferably greater than about 1 mm, and most preferably greater than about 2 mm so that a fluid can flow through the opening. The size of the fluid passage may be sufficiently small so that the fluid passage does not occupy a large volume of space (e.g., that could otherwise be occupied by a thermal energy storage material). Preferably the fluid passage has a size less than about 20 mm. For example, the fluid passage may a generally circular cross-section with a radius that is preferably less than about 10 mm.

It will be appreciated that a capsular structure having one or more sealed spaces and a fluid passage may be formed from a single component having a fluid passage such as shown by reference number 16, such as shown in the article 10 illustrated in FIG. 1A, or by assembling and/or arranging a plurality of segments 2 which together provide generally the same shape, such as the capsular structure 10′ illustrated in FIG. 1B. As such, a layer of capsules, including one or more sealed spaces, may be provided by a single segment or by a plurality of segments 2. A capsular structure may advantageously be provided by a plurality of segments so that the stresses in the structure (hoop stresses, or otherwise) are reduced or eliminated. A capsular structure may advantageously be provided by a plurality of segments so that a failure (e.g., a leak or puncture) of a sealed space results in a reduced loss of thermal energy storage material. If the capsular structure is formed by a plurality of segments, the number of segments may be two or more three or more, about four or more, or about six or more. The number of segments preferably is about 100 or less, more preferably about 30 or less, and most preferably about 10 or less. It will be appreciated that more than 100 segments may be employed when the capsular structure is large (e.g., greater than about 500 mm in one or more directions), or when the thermal energy storage material in the capsular structure is desired to be compartmentalized into 100 or more sealed spaces. A segment of a capsular structure, such as the segment 2 of a capsular structure 10 illustrated in FIG. 1B, may have a top surface and a bottom surface that forms a portion of the top surface 4 and bottom surface 6 of the capsular structure. A segment of a capsular structure, such as the segment 2 of a capsular structure 10 illustrated in FIG. 1B, may have an edge surface that becomes a portion of the outer edge surface 8 of the capsular structure. A segment of a capsular structure, such as the segment 2 of a capsular structure 10 illustrated in FIG. 1B, may have an edge surface that forms a portion of the opening of the capsular structure. A segment of a capsular structure, such as a segment 2 of a capsular structure 10 illustrated in FIG. 1B, may have one or more edges (e.g., two edges) that each mate with an edge of an adjacent segment.

Two or more segments of a capsular structure (e.g., two segments that share a common edge), or even all of the segments, may include the same thermal energy storage material or may include two or more different thermal energy storage materials. Preferably the segments in a capsular structure include a plurality of segments having the same thermal energy storage material. More preferably, all of the segments in the capsular structure have the same thermal energy storage material.

A pair of adjacent segments may have the same shape, volume, or both, or may have different shape, volume, or both. Preferably the capsular structure includes adjacent segments having generally the same volume. Preferably, the capsular structure includes adjacent segments generally having the same thickness. More preferably, the capsular structure includes adjacent segments generally having the same shape and size. Most preferably, the capsular structure includes, consists essentially of, or consists of adjacent segments having the same shape, size, and volume.

When a capsular structure includes two or more segments, it may be necessary to arrange the segments so that fluid flow between the edges of adjacent segments is reduced, minimized, or even eliminated. It will be appreciated that if adjacent segments are separated by a gap, a fluid (e.g., a heat transfer fluid) may flow radially between the opening and the exterior periphery of the capsular structure and thus decrease the heat transfer along the top and bottom surfaces of the capsular structure. In various embodiments of the invention, adjacent segments in a capsular structure may be shaped and/or arranged with mating edges so that the flow of heat transfer fluid between the adjacent segments is reduced, minimized, or eliminated. Preferably the adjacent segments have edges that generally mate.

The shape of the capsular structure and/or article may be defined by the packaging space and may be oddly shaped. The article may include a cover sheet (i.e., a cover sheet) having a top surface and a generally opposing base sheet having a bottom surface. The cover sheet (e.g., the top surface of the cover sheet), the base sheet (e.g., the bottom surface of the base sheet), or both, may have a portion that is (or may be) generally flat (e.g., have a generally planar surface), generally arcuate, or any combination thereof. Preferably the base sheet and/or the bottom surface of the base sheet includes a generally arcuate portion or is generally arcuate, and the top surface of the article is generally planar (e.g., the cover sheet is generally flat).

The cover sheet and the base sheet both include one or more openings. The cover sheet and the base sheet are arranged so that at least one opening of the cover sheet overlaps at least one opening of the base sheet. As such, the cover sheet and the base sheet have one or more corresponding openings. The cover sheet has an outer periphery in the regions furthest from the center of the cover sheet. The cover sheet has one or more opening peripheries in the region of the cover sheet near an opening (preferably near the center) of the cover sheet. The base sheet has an outer periphery in a region far from the center of the base sheet and an opening periphery near the opening (preferably near the center) of the base sheet. Each of the cover sheet and the base sheet may be sealingly attached to each other or to one or more other optional sub-structures (such as an outer ring) along the respective outer peripheries of the sheets, for forming one or more sealed spaces therebetween. Each of the cover sheet and the base sheet may be sealingly attached to each other or to one or more other optional sub-structures (such as an inner ring) along the respective opening peripheries of the sheets, for forming one or more sealed spaces therebetween. Preferably the cover sheet and the base sheet are sealingly attached to each other along their respective outer peripheries, along at least one of their respective corresponding opening peripheries, or both. Most preferably the cover sheet and the base sheet are sealingly attached to each other both along their respective outer peripheries and along at least one of their respective corresponding opening peripheries. It will be appreciated that the cover sheet and the base sheet may also be sealingly attached to each other or to one or more other optional sub-structures along one or more additional regions (other than their peripheries) so that a plurality of sealed spaces are formed.

The capsular structure may optionally include one or more sub-structures that when sealingly attached to a base sheet and a cover sheet forms one or more sealed spaces. The one or more sub-structure may be employed to form one or more walls that separates one or more sealed spaces from a heat transfer fluid. For example, the capsular structure may include an outer ring that provides a wall to isolate one or more sealed spaces from a heat transfer fluid along one or more side surfaces of the capsular structure. As another example, the capsular structure may include an inner ring that provides a wall to isolate one or more sealed spaces along at least a portion of the fluid passage through the capsular structure. If employed, the inner ring may have any geometry capable of being sealingly attached to an opening periphery of the base sheet, an opening periphery of the cover sheet and preferably both. Preferably the inner cross-section of the inner ring has a similar size and shape as the opening of the cover sheet, the base sheet, or both. If employed, the outer ring may have any geometry that can be sealingly attached to the outer periphery of the base sheet, the outer periphery of the cover sheet and preferably both. Preferably the outer cross-section of the ring has a similar size and shape as the outer circumference of the cover sheet, the base sheet, or both. The one or more sub-structures may be employed to form one or more walls that separates or provides a fluid isolation between two or more sealed spaces. For example, the one or more sub-structures may include one or more generally radial walls, one or more generally cylindrical walls, and the like. As another example, the one or more sub-structures may include a honeycomb or other open cell structure, such as described in paragraph 0084 of U.S. Patent Application Publication No. 2009-0250189 by Bank et al., published on Oct. 8, 2009, incorporated herein by reference. The wall thickness of the one or more sub-structures (e.g., inner ring, outer ring, or open cell structure) should be sufficiently thick to contain the thermal energy storage material, to support the structure, or both. The wall thickness of the one or more sub-structures preferably is greater than about 1 μm, and more preferably greater than about 10 μm. The wall thickness of the one or more sub-structures (e.g., inner ring, outer ring, or open cell structure) should be sufficiently thin so that a large portion of the volume and/or weight of the article can be the thermal energy storage material The wall thickness of the one or more sub-structures preferably is less than about 5 mm, more preferably less than about 1 mm, and most preferably less than about 0.2 mm.

The thickness of the capsular structure is defined by the average separation between the top surface of the article (e.g., the top surface of the cover sheet) and the bottom surface of the article (e.g., the bottom surface of the base sheet). The article may have a geometry so that heat can be rapidly provided from a fluid to thermal energy storage material and/or rapidly removed from the thermal energy storage material to a fluid. For example, the article may be relatively thin (e.g., compared with the length or diameter of the article). Preferably, the thickness of the article is less than about 80 mm, more preferably less than about 20 mm, even more preferably less than about 10 mm and most preferably less than about 5 mm. The thickness of the article preferably is greater than about 0.5 mm, more preferably greater than about 1 mm.

The longest dimension of the article (e.g., the length or diameter of the article) is typically much greater than the thickness of the article so that the article can both have a large volume (e.g., for containing a large volume of thermal energy storage material), and a large surface area (e.g., for rapid transfer of thermal energy). The longest dimension of the article preferably is greater than about 30, more preferably greater than about 50 mm and most preferably greater than about 100 mm. The longest dimension is defined by the use, and can be any length that meets the need for heat storage, heat transfer, or both, a particular use. The longest dimension of the article typically is less than about 2 m (i.e., 2,000 mm), however articles having longest dimension greater than about 2 m may also be employed.

The article may have one or more side surfaces. For example the article may have one or more side surfaces that are nonplanar. The article may have a single side surface that is generally arcuate, generally nonplanar, generally continuous, or any combination thereof. Preferably the one or more side surfaces are generally equidistant from a center of the article so that the article can be placed in a container having a generally cylindrical cavity with a cavity diameter that is only slightly larger than the average diameter of the article. When the ratio of the cavity diameter to the average diameter of the article is low, a large amount of the cavity is occupied by the article. For example, the ratio of the cavity diameter to the average diameter of the article may be less than about 1.8, preferably less than about 1.2, more preferably less than about 1.1, and most preferably less than about 1.05. It will be appreciated that the ratio of the cavity diameter to the average diameter of the article is typically at least about 1.0 (e.g., at least about 1.001).

A large portion of the volume of the capsular structure is the encapsulated volume (i.e. the volume of the one or more sealed spaces) so that the article can contain a relatively large amount of the thermal energy storage material. The total volume of the one or more sealed spaces of the article is preferably at least about 50 volume percent, more preferably at least about 80 volume percent, even more preferably at least about 85 volume percent and most preferably 90 volume percent based on the total volume of the article. The total volume of the one or more sealed spaces of the article is typically less than about 99.9 volume percent based on the total volume of the article. The remaining volume, not occupied by the thermal energy storage material, may include or consist substantially entirely of the capsular structure, void spaces (e.g., containing one or more gases), one or more structures for improving the heat transfer between the thermal energy storage material and the capsular structure, or any combination thereof. Structures for improving heat transfer between the thermal energy storage material and the capsular structure include any structure formed of a material having a relatively high thermal conductivity (e.g., relative to the thermal energy storage material) that is capable of increases the rate of heat flow from the thermal energy storage material to a heat transfer fluid. Suitable structures for improving the rate of heat flow include fins, wire mesh, protrusions into the sealed space, and the like.

The article preferably is easy to stack with other identical shaped articles, or other articles having a generally mating surface. For example, two articles to be stacked may have opposing surfaces that are generally mating surfaces so that when stacked, the two articles nest together. It will be appreciated that one approach for stacking articles so that they easily nest together is to select a shape (e.g., a shape of an arcuate surface, a shape of the sealed spaces, or both) having a rotational symmetry of a high order. The rotational symmetry may be about an axis in the stacking direction (e.g., an axis through the fluid passage of the capsular structure). The order of the rotational symmetry typically describes the number of distinct rotations between the two surfaces being stacked together in which they will nest together. The order of the rotational symmetry of the article, the base sheet (e.g., the arcuate surface, of the, base sheet), or both, preferably is at least 2, more preferably at least 3, even more preferably at least 5, and most preferably at least 7.

In one particularly preferred embodiment of the invention, adjacent layers (e.g., adjacent capsular structures) do not nest together. For example, a top surface of a first layer (e.g., of a first capsular structure) may be in contact with a bottom surface of a second layer (e.g., of a second capsular structure). The contacting top surface, bottom surface, or both may have one or more radial grooves or radial channels (i.e., a groove or channel that has a radial component (i.e., the orientation of at least a portion of the groove or channel includes a projection onto the radial direction), and preferably extends from the center opening to the outer periphery of the capsular structure) that allows for a heat transfer fluid to flow between the two surfaces. For example, the cover sheet of the first layer and the base sheet of the second layer may have a straight groove or channel that extends in a straight line form the opening to the outer periphery. In addition to having a radial component, a groove or channel may have a tangential component (i.e., the orientation of at least a portion of the groove or channel includes a projection onto the tangential direction). For example, a groove or channel may have a spiral shape that includes both a radial component and a tangential component. Two sheets in contact may have tangential components that are different (e.g., having different directions and/or different magnitudes) or the same. Tangential components of adjacent sheets may be arranged so that the fluid flowing between the adjacent sheets at least partially mixes. Advantageously, one sheet may have grooves or channels with a tangential component in the clockwise direction and the adjacent sheet may have grooves or channels with a tangential component in the counterclockwise direction, so that the fluid flowing between the two layers at least partially mixes when grooves intersect (e.g., when two streams of fluid flowing in the grooves of two adjacent capsular structures come into direct contact for less than their entire flow paths). FIG. 6A is a schematic drawing of a capsular structure 10 having a plurality of radial grooves 15 that extend between the opening of the structure 16 and the exterior periphery 19 of the structure. With reference to FIG. 6A, the grooves 15 may have one or any combination of the following features: be curved, the grooves may be curved so that they have a tangential component, the grooves may be uniformly spaced, adjacent grooves may have the same length, the grooves may have a spiral shape, and adjacent grooves may provide flow paths having the same hydraulic resistance. FIG. 6B is a schematic drawing showing the contact between a portion of a base sheet 30 of a first capsular structure and a portion of a cover sheet 28 of a second capsular structure. The two contacting surfaces may have generally different shapes or the same general shape, such as illustrated in FIG. 6B. As illustrated in FIG. 6B, the grooves of the contacting surfaces may have one or more intersections. As illustrated in FIG. 6B, the grooves of the first contacting surface may have a tangential portion and the grooves of the second contacting surface may have a tangential portion in an opposing direction relative to the first contacting surface. If grooves or channels are employed for providing a flow path, one or more surfaces may have any number of grooves or channels. Preferably, the number of grooves or channels in the capsular structure is sufficiently high and sufficiently distributed so that heat transfer fluid flowing between two layers (e.g., between two surfaces) can divided into a plurality of flow paths for efficiently removing heat. Adjacent flow paths may be the same or different. Preferably two or more flow paths (e.g., all of the flow paths) have generally the same length, generally the same hydraulic resistance, or both.

The capsular structure, such as the capsular structure illustrated in FIG. 6A, may have an opening 16, preferably at or near the geometric center of the capsular structure. The capsular structure includes one or more sealed spaces. The capsular structure may include a single sealed space, such as illustrated in FIG. 6A. The capsular structure may be generally thin and include a top surface 18, a bottom surface 20 an surface 22 near the exterior periphery 19 and an edge surface 24 near the opening. The capsular structure may include one or more features on the top surface, the bottom surface, or both that provides a flow path for a fluid to flow in at least a radial direction (e.g., when a plurality of capsular structures are stacked). Such a feature preferably extends from an opening periphery 21 of the capsular structure to an outer periphery 19 of the capsular structure. Such a feature may provide a flow direction that is generally arcuate, generally linear, or have regions that are linear and regions that are straight. As illustrated in FIG. 6A, the flow path may be provided by one or more channels or grooves that extend from the center periphery to the outer periphery. The grooves or channels in the top surface or bottom surface of the capsular structure may be distributed over the surface, so that each flow path (when a plurality of capsular structures are stacked) has generally the same hydraulic resistance. As illustrated in FIG. 6A, the grooves or channels may have a curvature such that the flow path has a tangential component in addition to the radial component. Such a curvature may be advantageous in preventing adjacent capsular structures from nesting together when identical capsular structures are stacked. For example, as illustrated in FIG. 6A, the capsular structure may be prepared by joining together a cover sheet and a base sheet having generally the same shape, and both having a plurality of curved grooves. When joined, the curved grooves in the top surface and the bottom surface are curved in opposite directions (when viewed from the top surface). As illustrated in FIG. 6A, the cover sheet and the base sheet may be sealed along the opening periphery and along the outer periphery, so that a sealed space is formed.

FIG. 6C, is a schematic drawing showing two adjacent segments 2 that form a portion of a capsular structure. As illustrated in FIG. 6C, each segment may include two sheets that are sealingly attached along a periphery of the segment. The location of the attachment may be on an edge surface 9. As illustrated in FIG. 6C, each segment may include one or more sealed spaces. Although no individual segment may have an opening, the segments may be arranged edgewise so that a capsular structure including an opening is formed. As illustrated in FIG. 6D, edges 9 of adjacent segments may mate when one segment is translated by a fraction of the thickness (e.g., half the thickness) relative to the adjacent segment.

The top surface of the capsular structure may be generally circular in shape, such as the top surfaces illustrated in FIGS. 1A and 6A. Other shapes for the top surface of the capsular structure are possible and may even be desirable. For example, the capsular structure may be employed in a heat storage device that is required to fit in a tight space, such as under the hood or under the floor of a vehicle. Although a cylindrical shape may be advantageous for reducing surface area other more elongated, or boxy shapes may be advantageous for fitting into a available space. It will be appreciated according to the teachings herein that the generally circular shaped surfaces of the capsular structure may advantageously be replaced with shapes that are not circular. As such, the capsular structure may have a top surface and/or a bottom surface having a generally oval shape, a generally rectangular shape, a generally square shape, a generally irregular shape, or any combination thereof. For example, the top surface and/or the bottom surface of the capillary structure may have a generally rectangular shape with rounded corners. FIG. 7 is a drawing showing illustrative features of a surface of a capsular structure. As illustrated in FIG. 7, the profile of the periphery of the top surface and the bottom surface of the capsular structure may have an elongated shape. For example the profile (of the outer periphery) of the top surface and the bottom surface may have a generally rectangular shape, a generally square shape, or a generally oval shape). It will be appreciated that the profile of the opening in the top surface may be any shape. The profile of the opening in the top surface and the profile of the outer periphery of the top surface may have shapes that are similar (but different size) or may have shapes that are different (such as a generally circular opening and a noncircular outer periphery). As illustrated in FIG. 7, the profile of the opening and the profile of the outer periphery may have the same shape, such as a generally oval shape.

The article preferably has a capsular structure that is difficult to bend. For example, the capsular structure may be free of a cross-section in which a cover sheet and a base sheet are in contact throughout most or even all of a length of the cross-section (such as a diameter of the capsular structure). There are venous approaches that may be employed for assuring that the capsular structure will be difficult to bend, including selecting an arrangement of the capsules so that the order of rotational symmetry is not an even number, selecting an arrangement of the capsules so that there is no rotational symmetry, selecting an arrangement of capsules including two or more rings of capsules (such as concentric rings) that are rotated relative to each other so that every radial section includes at least one sealed space, or any combination thereof. It will be appreciated that other geometries and other means may be employed to make the capsular article resistant to bending. For example, the materials for the capsular structure may be chosen to be generally stiff, the structure may include one or more ribs (e.g., in a tangential direction), and the like.

All of the thermal energy storage material of the article may be in a single sealed space. Preferably the thermal energy storage material of the article is divided between a plurality of sealed spaces so that if a sealed space is punctured or otherwise leaks, only a portion of the thermal energy storage material can be removed. As such, the number of sealed spaces in the article (e.g., sealed spaces that contain thermal energy storage material) is preferably at least 2, more preferably at least 3, and even more preferably at least about 5. The upper limit on the number of sealed spaces is practicalilty and for a particular application is defined by the need of the application. Nevertheless, the number of sealed spaces in the article typically is less than 1,000. However, it will be appreciated that very large articles may have 1,000 or more sealed spaces. For the same reasons, the volume fraction of the thermal energy storage material that is found in any single sealed compartment preferably is less than about 55%, more preferably less than about 38%, even more preferably less than about 29%, and most preferably less than about 21%, based on the total volume of the thermal energy storage material in the article. Typically a sealed space includes at least 0.1 volume % of the thermal energy storage material in the article. However, it will be appreciated that the article may include one or more sealed spaces that are substantially or even entirely free of the thermal energy storage material.

The sealed spaces may optionally be arranged in a plurality of concentric rings, including an innermost ring (e.g., a ring closest to the opening periphery) and an outermost ring (e.g., a ring closest to the outer periphery), each containing one or more sealed spaces. The sealed spaces in one ring may have a generally repeating pattern. For example, each sealed space or each groups of 2, 3, 4 or more sealed spaces in a ring may have generally the same shape and size. The number of sealed spaces in each ring may be the same or different. Preferably the outermost ring has more sealed spaces than the innermost ring, the average length of the sealed spaces of the outermost ring is less than the average length of the sealed spaces of the innermost ring (where the average length is measured in the radial direction from the opening to the outer periphery), or both, so that the volume variation between the sealed spaces of the outermost ring and the innermost ring is reduced.

As discussed hereinafter, the article may be placed in a container having a generally cylindrical shaped cavity, such as a (levity that is only slightly greater in dimension than the longest dimension of the article. For example, the diameter of the cavity of the container may be only slightly larger than the diameter of the capsular structure of the article. The diameter of the cavity should be sufficiently large so that the article can be inserted into the cavity. When the article (or a stack of the articles) is placed in the container, it may be desirable for a fluid to be capable of flowing between the outer periphery of the article and an interior wall of the container. This can be achieved by designing the relationship of the interior of the container and the shape of the article to create and maintain fluid flow paths. Any means of creating such fluid flow paths may be used. As such, the article may optionally have one or more indents along its periphery (e.g., the cover sheet and the base sheet may have one or more corresponding indents along their respective outer peripheries) so that a space is formed for flowing a heat transfer fluid. Alternatively, or in addition, the cavity of the container may have a surface with one or more grooves for flowing a fluid between the outer periphery of the article and the surface of the container. As another example, the diameter of the article may be sufficiently small in relation to the diameter of the interior of the cavity so that a fluid can flow along the entire outer periphery of the article. For example, the article may have one or more indents or the container may have one or more grooves, for each sealed space in the outermost ring of sealed spaces. An indent or a groove may have any shape, such as a polygonal shape, an arcuate shape, a wedge shape, and the like, provided it has a sufficient size to allow for the heat transfer fluid to flow. If employed, the smallest dimension of the indents and/or grooves is typically at least about 0.1 mm). It will be appreciated that a combination of two or more means of creating a fluid flow path may be used. For example, the article may have one or more indents along its outer periphery and the article may have a sufficiently small diameter so that fluid can flow along its entire outer periphery when placed in a cavity.

The base sheet may optionally have one or more protrusions, so that when the article is stacked with another article having a surface that generally mates with the base sheet, the two articles only partially nest. As such the one or more protrusions may function as a spacer to separate the generally mating surfaces so that a fluid (e.g., a heat transfer fluid) can flow between the mating surfaces. Stacking of articles and other spacing means are discussed hereinafter. If employed, the protrusions preferably cover only a small portion of the surface are of the base sheet so that the one or more protrusions do not substantially interfere with the flow of the fluid. The height of the protrusions may be selected to define the height (e.g., the average height) of the flow path between the two generally mating surfaces. The cover sheet preferably is free of such protrusions and has an outer surface that is generally flat so that two articles can be arranged with their over sheets in can contact generally over their entire top surfaces.

Thermal Energy Storage Material

Without limitation, suitable thermal energy storage materials for the heat storage device include materials that are capable of exhibiting a relatively high density of thermal energy as sensible heat, latent heat, or preferably both. The thermal energy storage material is preferably compatible with the operating temperature range of the heat storage device. For example the thermal energy storage material is preferably a solid at the lower operating temperature of the heat storage device, is at least partially a liquid (e.g., entirely a liquid) at the maximum operating temperature of the heat storage device, does not significantly degrade or decompose at the maximum operating temperature of the device, or any combination thereof. The thermal energy storage material preferably does riot significantly degrade or decompose when heated to the maximum operating temperature of the device for about 1,000 hours or more, or even for about 10,000 hours or more.

The thermal energy storage material may be a phase change material having a solid to liquid transition temperature. The solid to liquid transition temperature of the thermal energy storage material may be a liquidus temperature, a melting temperature, or a eutectic temperature. The solid to liquid transition temperature should be sufficiently high so that when the thermal energy storage material is at least partially or even substantially entirely in a liquid state enough energy is stored to heat the one or more objects to be hosted to a desired temperature. The solid to liquid transition temperature should be sufficiently low so that the heat transfer fluid, the one or more objects to be heated, or both, are not heated to a temperature at which it may degrade. As such the desired temperature of the solid to liquid transition temperature may depend on the object to be heated and the method of transferring the heat. For example, in an application that transfers the stored heat to an engine (e.g., an internal combustion engine) using a glycol/water heat transfer fluid, the maximum solid to liquid transition temperature may be the temperature at which the heat transfer fluid degrades. As another example, the stored heat may be transferred to an electrochemical cell of a battery using a heat transfer fluid where the heat transfer fluid has a high degradation temperature, and the maximum solid to liquid temperature may be determined by the temperature at which the electrochemical cell degrades or otherwise fail. The solid to liquid transition temperature may be greater than about 30° C., preferably greater than about 35° C., more preferably greater than about 40° C., even more preferably greater than about 45° C., and most preferably greater than about 50° C. The thermal energy storage material may have a solid to liquid transition temperature less than about 400° C., preferably less than about 350° C., more preferably less than about 200° C., even more preferably less than about 250° C., and most preferably less than about 200° C. It will be appreciated that depending on the application, the solid to liquid transition temperature may be from about 30° C. to about 100° C., from about 50° C. to about 150° C., from about 100° C. to about 200° C., from about 150° C. to about 250° C., from about 175° C. to about 400° C., from about 200° C. to about 375° C., from about 225° C. to about 400° C., or from about 200° C. to about 300° C.

For some applications, such as transportation related applications, it may desirable for the thermal energy material to efficiently store energy in a small space. As such, the thermal energy storage material may have a high heat of fusion density (expressed in units of megajoules per liter), defined by the product of the heat of fusion (expressed in megajoules per kilogram) and the density (measured at about 25° C. and expressed in units of kilograms per liter). The thermal energy storage material may have a heat of fusion density greater than about 0.1 MJ/liter, preferably greater than about 0.2 MJ/liter, more preferably greater than about 0.4 MJ/liter, and most preferably greater than about 0.6 MJ/liter. Typically, the thermal energy storage material has a heat of fusion density less than about 5 MJ/liter. However, thermal energy storage materials having a higher heat of fusion density may also be employed.

For some applications, such as transportation related applications, it may be desirable for the thermal energy storage material to be light weight. For example, the thermal energy storage material may have a density (measured at about 25° C.) less than about 5 g/cm³, preferably less than about 4 g/cm³, more preferably less than about 3.5 g/cm³, and most preferably less than about 3 g/cm³. The lower limit on density is practicality. The thermal energy storage material may have a density (measured at about 25° C.) greater than about 0.6 g/cm³, preferably greater than about 1.2 g/cm³, and more preferably greater than about 1.7 g/cm³.

The sealed spaces may contain any art known thermal energy storage material. Examples of thermal energy storage materials that may be employed in the thermal energy storage material compartments include the materials described in Atul Sharma, V. V. Tyagi, C. R. Chen, D. Buddhi, “Review thermal energy storage with phase change materials and applications”, Renewable and Sustainable Energy Reviews 13 (2009) 318-345. and in Belen Zalba, Jose Ma Marin, Luisa F. Cabeza, Harald Mehling, “Review on thermal energy storage with phase change: materials, heat transfer analysis and applications”, Applied Thermal Engineering 23 (2003) 251-283, both incorporated herein by reference in their entirety. Other examples of suitable thermal energy storage materials that may be employed in the heat transfer device include the thermal energy storage materials described in U.S. patent application Ser. No. 12/389,416 entitled “Thermal Energy Storage Materials” and filed on Feb. 20, 2009; and U.S. patent application Ser. No. 12/389,598 entitled “Heat Storage Devices” and filed on Feb. 20, 2009.

The thermal energy storage material may include an organic material, an inorganic material or a mixture of an organic and an inorganic material that exhibits the solid to liquid transition temperature, the heat of fusion density density, or both, described hereinbefore. Organic compounds that may be employed include paraffins and non-paraffinic organic materials, such as a fatty acid. Inorganic materials that may be employed include salt hydrates and metallics. The thermal energy storage material may be a compound or a mixture (e.g., a eutectic mixture) having a solid to liquid transition at generally a single temperature. The thermal energy storage material may be a compound or a mixture having a solid to liquid transition over a range of temperatures (e.g., a range of greater than about 3° C., or greater than about 5° C.).

Without limitation, suitable non-paraffinic organic materials for use as a thermal energy storage material include acids, alcohols, aldehydes, amides, organic salts, mixtures thereof and combinations thereof. By way of example, the non-paraffinic organic materials that may be used alone or as a mixture include polyethylene glycol, capric acid, eladic acid, lauric acid, pentadecanoic acid, tristearin, myristic acid, palmatic acid, stearic acid, acetamide, methyl fumarate, formic acid, caprilic acid, glycerin, D-lactic acid, methyl palmitate, camphenilone, docasyl bromide, caprylone, phenol, heptadecanone, 1-cyclohexylooctadecane, 4-heptadacanone, p-joluidine, cyanamide, methyl eicosanate, 3-heptadecanone, 2-heptadecanone, hydrocinnamic, cetyl alcohol, nepthylamine, camphene, o-nitroaniline, 9-heptadecanone, thymol, methyl behenate, diphenyl amine, p-dichlorobenzene, oxolate, hypophosphoric, o-xylene dichloride, chloroacetic, nitro naphthalene, trimytristin, heptaudecanoic, bees wax, glyolic acid, glycolic acid, p-bromophenol, azobenzene, acrylic acid, dinto toluent, phenylacetic acid, thiosinamine, bromcamphor, durene, benzylamine, methyl brombrenzoate, alpha napthol, glautaric acid, p-xylene dichloride, catechol, quinone, acetanilide, succinic anhydride, benzoic acid, stibene, benzamide, or any combination thereof.

Without limitation, the thermal energy storage material may include one or more inorganic salts selected from the group consisting of nitrates, nitrites, bromides, chlorides, other halides, sulfates, sulfides, phophates, phosphites, hydroxides, carboxides, bromates, mixtures thereof, and combinations thereof. By way of example, the thermal energy storage material may include, or consist substantially of K₂HPO₄.6 H₂O, FeBr₃.6H₂O, Mn(NO₃)₂.6 H₂O, FeBr₃ ₃.6 H₂O, CaCl₂.12 H₂O, LiNO₃.2 H₂O, LiNO₃.3 H₂O, Na₂CO₃.10 H₂O, Na₂SO₄.10 H₂O, KFe(SO₃)₂.12 H₂O, CaBr₂.6 H₂O, LiBr₂.2 H₂O, Zn(NO₃)₂.6 H₂O, FeCl₃.6 H₂O, Mn(NO₃)₂.4 H₂O, Na₂HPO₄.12 H₂O, CoSO₄.7 H₂O, KF.2 H₂O, Mgl₂.8 H₂O, Cal₂.6 H₂O, K₂HPO₄.7 H₂O, Zn(NO₃)₂.4 H₂O, Mg(NO₃).4 H₂O, Ca(NO₃).4 4 H₂O, Fe(NO₃)₂.9 H₂O, Na₂SiO₃.4 H₂O, K₂HPO₄.3 H₂O, Na₂S₂O₃.5 H₂O, MgSO₄.7 H₂O, Ca(NO₃)₂.3 H₂O, Zn(NO₃)₂.2 H₂O, FeCl₃.2 H₂O, Ni(NO₃)₂.6 H₂O, MnCl₂.4 H₂O, MgCl₂.4 H₂O, CH_(c)COONa.3 H₂O, Fe(NO₃)₂.6 H₂O, NaAl(SO₄)₂.10 H₂O, NaOH.H₂O, Na₃PO₄.12 H₂O, LiCH₃COO.2 H₂O, Al(NO₃)₂.9 H₂O, Ba(OH)₂.8 H₂O, Mg(NO₃)₂.6 H₂O, KAI (SO₄)₂.12 H₂O, MgCl₂.6 H₂O, or any combination thereof. It will be appreciated that inorganic salts having higher or lower concentrations of water may be used.

The thermal energy storage material may include or may even consist essentially of or consist of) at least one first metal containing material, and more preferably a combination of the at least one first metal containing material and at least second metal containing material. The first metal containing material, the second metal containing material, or both, may be a substantially pure metal, an alloy such as one including a substantially pure metal and one or more additional alloying ingredients (e.g., one or more other metals), an intermetallic, a metal compound (e.g., a salt, an oxide or otherwise), or any combination thereof. One preferred approach is to employ one or more metal containing materials as part of a metal compound; a more preferred approach is to employ a mixture of at least two metal compounds. By way of example, a suitable metal compound may be selected from oxides, hydroxides, compounds including nitrogen and oxygen (e.g., nitrates, nitrites or both), halides, or any combination thereof. It is possible that ternary, quaternary or other multiple component material systems may be employed also. The thermal energy storage materials herein may be mixtures of two or more materials that exhibit a eutectic.

The volume of the thermal energy storage material in the one or more sealed spaces of the article is sufficiently high so that the article can store a large amount of thermal energy. The ratio of the volume of the thermal energy storage material contained in the article to the total volume of the one or more sealed spaces, the ratio of the volume of the thermal energy storage material to the total volume of the article, or both (the volumes measured at a temperature of about 25° C., or at a temperature at which the thermal energy storage material is a liquid) preferably is greater than about 0.5, more preferably greater than about 0.7, and most preferably greater than about 0.9. The ratio of the volume of the thermal energy storage material contained in the article to the total volume of the one or more sealed spaces, the ratio of the volume of the thermal energy storage material to the total volume of the article, or both (the volumes measured at a temperature of about 25° C., or at a temperature at which the thermal energy storage material is a liquid) is typically less than about 1.0, and more typically less than about 0.995.

The sealed space may include a volume that contains a gas, such air, N₂, or an inert gas such as He, Ar, and the like, so that the thermal energy storage material can expand when heated. For example, the sealed space may have a region that is free of thermal energy storage material at a temperature of about 25° C., so that upon heating the thermal energy storage material above its liquidus temperature, the thermal energy storage material can expand without forming a hole in the cover sheet or base sheet or causing one or more sheets to delaminate. The volume of a sealed space that is free of thermal energy storage material (e.g., the volume of the sealed space that contains a gas) at 25° C., may be at least about 0.5%, preferably at least about 1%, and most preferably at least about 1.5%, based on the total interior volume of the sealed space.

FIG. 2A is a drawing that illustrates features of an article 10 that includes a capsular structure having a single sealed space (i.e., a single capsule). The capsular structure includes a cover sheet 28 having an opening 29 and a base sheet 30 having an opening 31. The opening of the cover sheet 29 and the opening of the base sheet 31 overlap each other (e.g., completely overlap) and are thus corresponding openings. The cover sheet 28 and the base sheet are sealingly attached to an outer ring 32. As illustrated, the outer periphery of the cover sheet 28, the outer periphery of the base sheet, or preferably both may be sealingly attached to the outer ring 32. The cover sheet has a top surface 18 that is an exterior surface of the article 10, and an opposing surface that is generally on the interior of the article 10. The base sheet has a bottom surface 20 that is generally an exterior surface of the article 10, and an opposing surface that is generally on the interior of the article. The capsular structure may also have an inner ring 34 that is sealingly attached to an opening periphery of the cover sheet 28, an opening periphery of the base sheet 30 or preferably both. As illustrated, the outer ring 32 may have a generally cylindrically shaped outer surface and a generally cylindrically shaped inner surface, the inner ring 34 may have a generally cylindrically shaped outer surface and a generally cylindrically shaped inner surface, the cover sheet 28 (e.g., the top surface 18 of the cover sheet) may have a generally circular shape, the base sheet 30 (e.g., the bottom surface of the base sheet) may have a generally circular shaped circumference, or any combination thereof. One of any combination of the following openings may have a generally cylindrical shape: the fluid passage of the article 16, the opening of the cover sheet 29, and the opening of the base sheet 31. It will be appreciated that a cross-section of an opening may have a different shape, such as a polygonal shape, or a different arcuate shape (e.g., an oval shape).

As illustrated in FIG. 2A, the article 10 may have have a single side surface 22 that is generally arcuate, generally nonplanar, and generally continuous. Such a side surface may be generally equidistant from the center of the article so that the article can be placed in a container having a generally cylindrical cavity with a cavity diameter that is only slightly larger than the average diameter of the article.

An illustrative cover sheet 28 having an opening 29 for use in the article, is shown in FIG. 2B. It will be appreciated that the opening in the cover sheet may be formed prior to, during, or after attaching (e.g., sealingly attaching) the cover sheet to one or more other sheets or one or more other sub-structures. The cover sheet may have an outer periphery 19 that is generally circular, an inner or opening periphery 21 that is generally circular, or both. The cover sheet 28 may have a bottom surface 38 that is generally flat and an opposing top surface 18 that is generally flat. The cover sheet 28, may be formed from one or more encapsulant materials 12. As illustrated in FIG. 2B, the outer periphery 19 of the cover sheet 28 may include a region 23 on the bottom surface 38 of the cover sheet 28, near the outer perimeter of the cover sheet. Referring to FIGS. 2A and 2B, the base sheet 28 may be sealingly attached along the region 23 of the outer periphery 19 on the bottom surface 38. The encapsulant material for the top surface 18 preferably is a material that resists corrosion when in contact with the heat transfer fluid. The encapsulant material for the bottom surface 38 preferably is a material that resists corrosion when in contact with the thermal energy storage material. The encapsulant material for the top surface 18 and the bottom surface 38 may be the same material or different materials. The top surface 18, except for the opening 29 may have a generally circular shape. The thickness of the rover sheet 28, as measured by the distance between the top surface 18 and the bottom surface 38 of the cover sheet may be generally uniform. The standard deviation of the thickness of the cover sheet 28 is preferably less than about 15%, more preferably less than about 10%, and most preferably less than about 3% of the average thickness of the cover sheet.

FIG. 2C illustrates a cross-section of the article 10 of FIG. 2A, taken perpendicular to the top surface 18 of the cover sheet 28. As illustrated in FIG. 2C, the article may have one or more sealed spaces 14 that includes thermal energy storage material 26. The sealed space may include an unfilled volume 27, i.e., a volume contains a gas. The unfilled volume 27 may allow for the thermal energy storage material to expand when it is heated, such as when the temperature of the thermal energy storage material increases, when the thermal energy storage material undergoes a solid to liquid phase transition, or both. The cover sheet, the base sheet, the outer ring, the inner ring, or any combination thereof preferably includes one or more encapsulant materials that resists corrosion when contacted with the thermal energy storage material (e.g., on an interior surface), one or more encapsulant materials that resist corrosion when contacted by a heat transfer fluid, (e.g., on an exterior surface), or both. The cover sheet, the base sheet, the outer ring, the inner ring, or any combination thereof most preferably include or consist substantially entirely of the same one or more encapsulant materials. The cover sheet 28 and the base sheet 30 are both sealingly attached along both their outer peripheries 19 and their opening peripheries 21 for forming the one or more sealed spaces 14.

FIG. 2D, illustrates a formed sheet 40 that may be employed as a base sheet for the article. The formed sheet may be embossed or otherwise formed so that it is generally arcuate and/or has a plurality of walls. The formed sheet has a trough region 43 that is capable of holding or containing a liquid. The formed sheet also has an opening 46, so that a fluid can flow through the formed sheet. The formed sheet preferably also has one or more generally flat regions such as one or more lip regions 44 that may be attached to a generally flat cover sheet such as a cover sheet described in FIG. 2B). The one or more lip regions 44 preferably are coplanar. The formed sheet 40 is not a generally flat sheet. For example, the formed sheet 40 may have a bottom well that includes a top surface 41 and a generally opposing bottom surface 42. The formed sheet may have a side all extending from the bottom wall. The side wall may include a side surface 49 that is generally arcuate. The formed sheet 40 may have an opening wall extending from an interior periphery of the bottom wall. The opening wall may have an opening surface 48 that is generally arcuate and partially or totally defines the fluid passage through the article. The formed sheet has an outer periphery 45 and an opening periphery 47. The outer periphery 45, the opening periphery 47, or preferably both are lip regions 44. It will be appreciated that the formed sheet may include a transition region connecting the bottom wall and the side wall, or the bottom wall and side wall may be combined into one arcuate wall. It will be appreciated that the formed sheet may include a transition region connecting the bottom wall and the opening wall, or the bottom wall and opening wall may be combined into one arcuate wall.

As described hereinbefore, the capsular structure may include a plurality of segments that are arranged to form the capsular structure having one or more sealed spaces and one or more fluid passages. FIGS. 3A, 3B, and 4 are illustrative side views of adjacent segments of capsular structures. As illustrated in FIGS. 3A, 3B and 4, adjacent segments may have mating edges 9 (i.e., edges surfaces that generally mate). The segments may mate when the adjacent segments are arranged in a coplanar orientation, such as shown by segments 2′, 2″ in FIGS. 3A and 3B, where surfaces 4′ and 6′ of the two segments are generally coplanar. The edges of adjacent segments may mate when the two adjacent segment are shifted, so that their top and bottom surfaces 4′ and 6′ are not coplanar. For example, the one segment may be shifted by half the thickness of the segment 2′″, as illustrated in FIG. 4. As such, the mating edge 9 of a first segment may mate with portions of the edges of two stacked segments that are both adjacent to the first segment. As illustrated in FIG. 4, one stack of segments may include one or more (e.g., two) fractional segments 3, such as a fractional segment having half the height of the other segments 2′″.

It will be appreciated that some or all of the troughs of the formed sheet 40′ may be partially or substantially entirely filled with a thermal energy storage material, and a generally flat cover sheet (such as described in FIG. 2B) can be placed over the troughs so that the cover sheet generally contacts the lip region. The cover sheet may be sealingly attached to the formed sheet in some or even all of the lip regions for forming a plurality of sealed spaces containing the thermal energy storage material. As shown in FIG. 5A and 5B, the formed sheet 40′ may have a pattern of troughs so that the bottom surface 41′ of a first formed sheet 40 is generally a mating surface of a bottom surface 41′ of an identical second formed sheet 40′. As such, two articles made using the formed sheet 40′ are capable of being stacked with their bottom surfaces 41′ opposing each other so that the two articles will at least partially nest.

FIG. 5B is a schematic drawing of a portion of a formed sheet 40′ (e.g., a base sheet) that may be employed in an article having a plurality of sealed spaces. The formed sheet has an opening 46 near the center of the sheet, which may be a generally circular opening. FIG. 5B shows only ¼ of the formed sheet and thus only ¼ of the opening is shown. FIG. 5B shows the bottom surface 41′ of the formed sheet 40′. The formed sheet has a plurality of trough regions 43′ and a plurality of lip regions 44′. The trough regions 43′ may be arranged in a plurality of rings of troughs 50. As illustrated, the formed sheet may have an innermost ring of troughs 50′ and an outermost ring of troughs 50″. The formed sheet may also have one or more additional rings of troughs 50′″, between the innermost and the outermost rings of troughs 50′, 50″. As illustrated in FIG. 5B, some or all of the troughs in a ring, or even some or all of the troughs in different rings may have about the same shape, about the same volume, or even be substantially congruent. It will be appreciated that the number of troughs in the innermost ring of troughs may be more than, less than or the same as the number of troughs in the outermost ring of troughs. Preferably, the number of troughs in the innermost ring of the formed sheet 40′ is less than the number of troughs in the outermost ring, as illustrated in FIG. 5B. Some, or preferably all of the troughs regions 43′ have a lip region 44′ around the trough region. As such, a trough region 43′ may be separated by the other trough regions by a lip region 44′. The formed sheet 40; has an outer periphery 45′. As illustrated in FIG. 5B, the formed sheet may have one or more indents 51 near the outer periphery 45. The one or more indents may be used for flow channels or flow paths along the outer periphery. Preferably the outer perimeter of the bottom surface of the formed sheet has a generally circular shape (excluding the optional one or more indents). As illustrated in FIG. 5B, the outer periphery, the inner periphery, and preferably both, may be lip regions 44′.

FIG. 5A shows an illustrative relationship between a capsular structure 10′ (e.g., a formed sheet 40′ of a capsular structure) and a container 68. The container 68 may have an inner wall 60, an outer wall 62, an insulating layer 64, or any combination thereof. With reference to FIG. 5A, the container 68 may have, an insulating layer 64 interposed between two walls, 60, 62. The inner wall 60 of the container has a larger diameter than the diameter of the formed sheet so that the formed sheet can fit within the container. A flow path between the periphery of the sheet and the inside wall of the container may include one or more indents 51 in the formed sheet 40′, a gap 52 formed by the differences in the sizes (e.g., the diameters) of the formed sheet 40′ and the cavity of the container, one or more grooves 53 in an inside wall 60 of the container, or any combination thereof.

Stack of Articles

The articles containing he thermal energy storage material preferably are capable of being stacked either with other identical articles or with a second article having a generally mating surface (such as a generally mating base sheet). The articles are stacked in axial layers with a space between adjacent axial layers so that a heat transfer fluid can flow between the axial layers. An axial layer will generally contain one, two or more article. An axial layer (e.g., each axial layer) preferably contains one or two articles. For example, an axial layer may have two articles that are in contact on a surface, such as a base surface or a cover surface, so that a fluid cannot generally flow between the two articles). As such, some of the articles (e.g., each article except the articles at an end of a stack) may have a first surface (e.g., a base surface) that is generally in complete contact with a surface of a first adjacent article so that a fluid cannot flow along the first surface, and a second surface that is separated from a second adjacent article (e.g., having an opposing surface that is generally a mating surface with the second surface) so that a fluid can flow along some, most, or even all of the second surface. The separation between two adjacent axial layers may be due to any art known spacing means. By way of example, suitable spacing means include one or more protrusions on a surface of at least one of the articles, a spacer material between, the two layers, a capillary structure between two layers, or any combination thereof. Preferably the second surface of the article has a generally arcuate shape and the article partially nests with the second adjacent article. The spacing between two articles that partially nest preferably is generally constant (except for the protrusions or other spacers that cause the adjacent articles to be separated). It will be appreciated that the stacking of the articles may include a step of rotating an axial layer (e.g., rotating an article), or otherwise arranging it so that the axial layer at least partially nests with an adjacent axial layer. The flow of a fluid between two opposing surfaces of two adjacent axial layers will generally be in a radial direction and may be described as a generally radial flow. Each pair of axial layers that are spaced apart will have a radial flow path. The stack of articles will typically have a plurality of radial flow paths (e.g., 2, 3, or more). Two or more (e.g., each radial flow path may have the same flow length, the same thickness, the same crass-sectional shape, or any combination thereof. For example, two or more (e.g., all) of the radial flow paths may be congruent. It will be appreciated that if the opening (i.e., fluid passage) is at the center of the article, the radial flow path may be generally symmetric, irrespective of the flow direction.

When stacked (e.g., in a stack containing 3, 4 or more articles), the articles preferably each have at least one opening that corresponds with an opening from each of the other articles (except possibly an article at one end of the stack), so that a portion of a fluid can flow from a first article in the stack to a last article in the stack by flowing through each of the corresponding openings of the articles interposed between the first and last article without flowing between adjacent articles (i.e., without a generally radial flow). The flow through the openings will generally be in an axial direction and may be described as a generally axial flow.

As described above, the stack of articles may define a central axial flow path (e.g., through the central axis formed by the openings of the articles) and one or more radial flow paths that are generally perpendicular to the central axial flow path.

The stack of articles will generally be tightly packed (e.g., except for the radial flow paths) so that the stack of articles is compact and contains a large amount of thermal energy storage material. As such, the radial flow path has a height (in the direction between the adjacent articles), e.g., an average height, that is generally small. The height of the radial flow path preferably is less than about 15 mm, more preferably less than about 5 mm, even more preferably less than about 2 mm, even more preferably less than about 1 mm, and most preferably less than about 0.5 mm. The height of the radial flow path typically is large enough so that the fluid can flow through the path. Typically the height (e.g., the average height) of the radial flow path is greater than about 0.001 mm (e.g., greater than about 0.01 mm).

FIG. 5C illustrates an aspect the invention that includes a plurality of articles 10′, each having one or more sealed spaces 14 for containing a thermal energy storage material. The articles 10′ may include a formed sheet 40″ having a generally arcuate surface 41″. The surface 41″ of one article may generally mate with the surface of a second article. The articles may be arranged so that adjacent articles partially nest together. The articles illustrated in FIG. 5C have a rotational symmetry of order 8 and thus can be rotated in 8 different positions so that they will partially nest. It will be appreciated that articles with a higher or a lower order of symmetry may be employed. As illustrated in FIG. 5C, the articles may have a generally circular cross-section. The outer periphery of each article may have a plurality of indents 51 that are large enough to allow for a fluid flow. The articles 10′ may have sealed spaces 14 arranged in one or more concentric rings of sealed spaces. Each article 10′ may have a fluid passage 46′ generally near the center of the article so that when the articles are stacked (e.g., stacked in an axial direction), an axial flow path 84′ is formed. The axial flow path 84′ preferably includes a fluid passage 46′ of each article 10′.

Heat Storage Device

The articles (e.g., a stack of articles) described herein may be employed in a heat storage device. The heat storage device may include a container or other housing having one or more orifices for flowing a heat transfer fluid into the container and one or more orifices for flowing a heat transfer fluid out of the container. The heat storage device has one or more heat transfer fluid compartments. Preferably, the heat storage device includes a single heat transfer fluid compartment. A heat transfer fluid compartment may include or consist substantially of a contiguous space in the container between the inlet and the outlet, where the heat transfer fluid can flow. The containers preferably is at least partially insulated so that heat losses from the container to the ambient may be reduced or minimized.

The heat storage device may be designed so that it contains a large concentration of thermal energy storage material, so that it can transfer thermal energy between a heat transfer fluid and the thermal energy storage material rapidly and/or uniformly, so that it is generally compact, so that it can store heat for a long time, or any combination thereof.

The inside of the container of the heat storage device may have any shape capable of holding a stack of articles. Preferably, the shape of the inside of the container is such that the stack of articles occupies a large portion of the interior volume of the container. The ratio of the total volume of thermal energy storage material (e.g., measured at about 25° C.) contained in the sealed spaces of the articles in the container to the total interior volume of the container (e.g., at a temperature of about 25° C.) may be greater than about 0.3, preferably greater than about 0.5, more preferably greater than about 0.6, even more preferably greater than about 0.7, and most preferably greater than about 0.8. The upper limit on the volume of thermal energy storage material in the container is the need for space for a heat transfer fluid that contacts the articles for transferring thermal energy. The ratio of the total volume of thermal energy storage material (e.g., measured at about 25° C.) contained in the sealed spaces of the articles in the container to the total interior volume of the container (e.g., at a temperature of about 25° C.) may be less than about 0.99, preferably less than about 0.95.

Heat Transfer Fluid Compartment/Flow Path

The heat storage device has a heat transfer fluid compartment for flowing a capable of containing a heat transfer fluid as it circulates through the device. The heat transfer fluid compartment preferably is connected to one or more orifices (e.g. one or more inlets) for flowing a heat transfer into the heat transfer fluid compartment. The heat transfer fluid compartment preferably is connected to one or more orifices (e.g., one or more outlets) for flowing a heat transfer out of the heat transfer fluid compartment. The heat transfer fluid compartment may be a space at least partially defined by one or more heat transfer fluid compartment walls, a space at least partially defined by one or more articles, a space at least partially defined by a housing or container of the heat storage device, or any combination thereof.

The heat transfer fluid compartment defines the flow path of a heat transfer fluid through the heat storage device. The heat transfer fluid compartment includes a generally axial flow path through the openings of the stack of articles. The heat transfer fluid compartment includes a generally radial flow path between two adjacent articles. It will be appreciated that the radial flow may be an inward flow from an outer periphery to the opening of an article, or an outward flow from an opening to the outer periphery of an article. The heat transfer fluid compartment includes a flow path having a generally axial component (and optionally a tangential component) between an outer periphery of the article and a wall of the container. Preferably the combined radial flow paths have a relatively high hydraulic resistance. For example, the combined radial flow paths has a hydraulic resistance that is greater than (more preferably at least two times greater than) the hydraulic resistance of the central axial flow path, the outer axial flow path, or both.

The heat transfer fluid compartment preferably has sufficient thermal communication with the sealed spaces containing the thermal energy storage material so that it can remove heat or provide heat to the thermal energy storage material. The heat transfer fluid compartment preferably is in direct thermal communication with one or more (or more preferably all) of the sealed spaces. A direct thermal communication can be any path of shortest distance between a sealed space and a portion of the heat transfer fluid compartment that is free of a material having low thermal conductivity. Low thermal conductivity materials include materials having a thermal conductivity less than about 100 W/(m·k), preferably less than about 10 W/(m·k), and more preferably less than about 3 W/(m·K). For example, the heat transfer fluid or the heat transfer fluid compartment may contact a wall of one or more (or preferably all) of the sealed, or be separated from the sealed spaces substantially or entirely by materials having high thermal conductivity (e.g., greater than about 5 W/(m·K), greater than about 12 W/(m·K), or greater than about 110 W/(m·K).

The heat transfer fluid compartment preferably is in direct thermal communication with one or more (or more preferably all) of the sealed spaces in the heat storage device. A direct thermal communication can be any path of shortest distance between a thermal energy storage compartment and a portion of the heat transfer fluid compartment that is free of a material having low thermal conductivity. For example, the heat transfer fluid or the heat transfer fluid compartment may contact a wall of one or more (or preferably all) of the sealed paces (such as a base sheet or a cover sheet), or be separated from the sealed spaces substantially or entirely by materials having high thermal conductivity (e.g., greater than about 5 V/(m·K), greater than about 12 W/(m·k), or greater than about 110 W/(m·K). It will be appreciated that a very thin layer (e.g., less than about 0.1 mm, preferably less than about 0.01 mm, and more preferably less than about 0.001 mm) of a material having a low thermal conductivity may be between the heat transfer fluid compartment and a thermal energy storage material compartment without appreciably affecting the heat transfer.

The size and shape of the sealed spaces and/or articles may be chosen to maximize the transfer of heat to and from the phase change material contained in the capsules. The average thickness of the article may be relatively short so that the heat can quickly escape from the center of the sealed space. The average thickness of the article, sealed space, or both may be less than about 100 mm, preferably less than about 30 mm, more preferably less than about 10 mm, even more preferably less than about 5 mm, and most preferably less than about 3 mm. The average thickness of the article, the sealed space, or both, may be greater than about 0.1 mm, preferably greater than about 0.5 mm, more preferably greater than about 0.8 mm, and most preferably greater than 1.0 mm.

The articles preferably have a relatively high surface area to volume ratio so at the area of contact with the heat transfer fluid is relatively high. For example, the article may have a surface that maximizes the contact with a heat transfer fluid compartment, the article may have a geometry that maximizes the transfer of heat between the capsule and the heat transfer fluid compartment, or both. The ratio of the total surface area of the interface between the heat transfer fluid compartment and the articles in the heat storage device to the total volume of the thermal energy storage material in the heat storage device may be greater than about 0.02 mm⁻¹, preferably greater than about 0.05 mm⁻¹, more preferably greater than about 0.1 mm⁻¹, even more preferably greater than about 0.2 mm⁻¹, and most preferably greater than about 0.3 mm⁻¹.

Container Housing

The heat storage device has a container for containing the stack of articles. The stack of articles may be contained in one or more cavities of the container. Suitable containers have one or more orifices (e.g., one or more inlets) for flowing a heat transfer fluid into the cavity of the container and one or more orifices (e.g., one or more outlets) for flowing a heat transfer fluid out of the cavity of the container. The inlet and the outlet may be on the same side or on different sides (e.g., opposing sides) of the heat storage device. Other than the orifices, the container preferably is sealed or constructed so that a fluid flowing through the container does not leak out of the container, so that a fluid flowing through the container may have a pressure greater than ambient pressure, or both.

The container may have any shape. Preferably, the container has a shape that can be filled with a large amount of thermal energy storage material in the (e.g., in the sealed spaces of the stack of articles) so that the heat storage device can store a large quantity of heat. Without limitation, the container and/or the cavity of the container may have a cross-section (e.g., perpendicular to the direction of stacking) that is generally circular, generally oval-shaped, generally rectangular, generally square-shaped, or have a different generally polygonal shape. In a particularly preferred embodiment, the container has a generally cylindrical shape, the cavity of the container has a generally cylindrical shape, or both. For example, the container of the heat storage device may have a generally cylindrical shaped inner surface, a generally cylindrical shaped outer surface, or both. A cylindrical shaped cavity may allow for efficient packing of articles having a generally circular cross-section in the cavity. By way of example, a generally cylindrically shaped articles has a generally circular cross-section. A cylindrical shaped article, a cylindrical shaped cavity, or both, may allow for efficient insulation of the heat storage device. Typically, the container may be characterized by a height in the direction of stacking of articles (i.e., the axial direction) and an average length (e.g., a diameter) in the direction perpendicular to the stacking direction. For example, a cylindrically shaped container may be characterized by a height and a diameter. The height to length (e.g. diameter) ratio of the container may be less than about 20, preferably less than about 5, more preferably less than about 3, and most preferably less than about 2. The height to length ratio (e.g., the height to diameter ratio) of the container may be greater than about 0.05, preferably greater than about 0.2, more preferably greater than at 0.33, even more preferably greater than about 0.5, and most preferably greater than about 0.6. The cavity of the container may be characterized by a height in the direction of stacking of the articles and an average length (e.g., a diameter) in the direction perpendicular to the stacking direction. Most preferably, the interior of the container has a generally cylindrical shaped cavity, characterised by a cavity diameter, a cavity height, and an axial center. The interior of the container may have a generally arcuate wall (having an arcuate surface) that is parallel to the axial direction of the cavity. As previously discussed, the arcuate surface preferably has a generally circular cross-section. The container may be employed to house a stack of the articles. The stack of articles is preferably arranged so that there is a central axial flow path (e.g., through fluid passages of a plurality of cavities) at or near the axial center of the cavity of the container. The outer periphery of the articles may include one or more indents, the interior wall of the container may have one or more grooves (preferably in an axial direction, or a direction having an axial component), the articles may have a length or diameter less than the cavity length or diameter, or any combination thereof, so that a heat transfer fluid can flow in an axial direction between the outer peripheries of the articles and the interior axial surface of the container. Such a flow may be described as an outer axial flow. The stack of articles preferably is arranged in the container so the the distance between the outer periphery of the articles and the arcuate interior surface of the container is generally uniform for different regions of an article and for different articles (except for any indents in the article or grooves in the wall of the container).

The heat storage device may be used in applications that require storing heat for long periods of time, storing heat in a generally cold environment (e.g., an environment having a temperature less than about 0° C., or even less than about −30° C.), or both. Preferably the heat stored in the heat storage device is slowly lost to the environment Therefore some form of insulation is preferably used in the present invention. The better the insulation of the system is, the longer is the storage time.

Any known form of insulation which reduces the rate of heat loss by the heat storage device may be utilized. For example, any insulation as disclosed in U.S. Pat. No. 6,689,751, incorporated herein of its entirety by reference, may be employed. The heat storage device preferably is (thermally) insulated container, such that it is insulated on one or more surfaces. Preferably, some or all surfaces that are exposed to ambient or exterior will have an adjoining insulator, The insulating material may function by reducing the convection heat loss, reducing the, radiant heat loss, reducing the conductive heat loss, or any combination. Preferably, the insulation may be through the use of an insulator material or structure that preferably has relatively low thermal conduction. The insulation may be obtained through the use of a gap between opposing spaced walls. The gap may be occupied by a gaseous medium, such as an air space, or possibly may even be an evacuated space (e.g., by use of a Dewar vessel), a material or structure having low thermal conductivity, a material or structure having low heat emissivity, a material or structure having low convection, or any combination thereof. Without limitation, the insulation may contain ceramic insulation (such as quartz or glass insulation), polymeric insulation, or any combination thereof. The insulation may be in a fibrous form, a foam form, a densified layer, a coating or any combination thereof. The insulation may be in the form of a woven material, a knit material, a nonwoven material, or a combination thereof. The heat transfer device may be insulated using a Dewar vessel, and more specifically a vessel that includes, generally opposing walls configured for defining an internal storage cavity, and a wall cavity between the opposing walls, which wall cavity is evacuated below atmospheric pressure. The walls may further utilize a reflective surface coating (e.g., a minor surface) to minimize radiant heat losses.

Preferably, a vacuum insulation around the heat storage device and or the heat storage system is provided. More preferably, a vacuum insulation as disclosed in U.S. Pat. No. 6,889,751, incorporated by reference herein in its entirety, is provided.

Compaction Means

The heat storage device may optionally include one or more compaction means to a stack of articles so that the spacing between layers is generally maintained. The compaction means may be any means capable of applying a compressive force to the stack of articles. The compressive force should be sufficiently high so that two articles do not rotate relative to each other, do not move axially relative to each other, or both. The compressive force may be sufficiently low so that an article is not permanently deformed, cracked, or both. Preferred means of compaction will allow for some changes in the thickness of the articles as the temperature of the thermal energy storage material changes, as the thermal energy storage material changes between a solid and a liquid phase, or both. By way of example, the one or more means of compaction may include one or more springs above the stack of articles, one or more springs below the slack of articles, or both. Without limitation, a means of compaction such as a spring, may be employed to reduce or minimize the change in the thickness of a radial flow path between two adjacent articles when the thermal energy storage material is heated, undergoes a phase transition (such as a solid to liquid transition) or both.

The heat storage device may have a plurality of flow paths for the flow of a heat transfer fluid through the device. Each flow path preferably includes at least one radial flow between two adjacent articles. Preferably two or more (e.g., each) of the flow paths through the heat storage device has a similar total length, a similar total hydraulic resistance, or both. For example, two or more (e.g., each of the flow paths may generally be characterized as a Tichelmann system. An orifice of the heat storage device may be connected to the openings of the stack of articles by a tube or other means so that the heat transfer fluid must flow through the axial path formed by the openings of the stack of articles. Typically a tube connecting an orifice to the axial flow path formed by the openings of the articles will extend to either one of the first (e.g., the first) article in a stack of articles or one of the last (e.g., the last) articles in a stack of articles. The device may include one or more seals or plates (e.g., at the top and/or bottom of the stack of articles) so that a heat transfer fluid flowing from an inlet to an outlet must flow through a radial flow path. A seal may include an opening for allowing a tube to connect an orifice to the opening of the stack of articles. A seal may be used to block the flow of the fluid at an end of an axial flow path along the openings of the stack of articles, to block the flow of a fluid at an end of an axial flow path along a periphery of the stack of articles, or both.

Method for Making the Capsular Structure

The capsular structure and the articles containing the thermal energy storage material may be formed using any method that provides for the encapsulation of the thermal energy storage material. Without limitation, the process may employ one or any combination of the following: cutting or punching an opening (e.g., a hole) through a cover sheet, cutting or punching an opening (e.g., a hole) through a base sheet (e.g., a thin sheet such as a foil), forming (e.g., thermoforming, stamping, embossing or otherwise deforming) a base sheet to define a pattern in the sheet including at least one depression or trough region, forming a base sheet to define a pattern in the sheet including one or more lip regions and one or more trough regions, cutting or punching an outer periphery (e.g., a generally circular outer periphery) on a be sheet, cutting or punching an outer periphery (e.g., a generally circular outer periphery) on a cover sheet, filling a trough (e.g., a trough formed from the base sheet) with a thermal energy storage material, covering a trough (e.g., a filled trough) with a cover sheet, sealingly attaching a cover sheet (e.g., to a base sheet) so that one or more sealed spaces containing thermal energy storage material are formed, sealingly attaching a base sheet along an outer periphery, sealingly attaching a base sheet along an opening periphery, sealingly attaching a cover sheet (e.g., to a base sheet) along an opening periphery, or sealingly attaching a cover sheet (e.g., to a base sheet) along an outer periphery. The process of forming the article preferably includes a step of stamping, embossing, or thermoforming a base sheet. The process of forming the article may employ one or more of the process steps for producing a capsule described in U.S. patent application Ser. No. 12/389,598 entitled “Heat Storage Devices” and filed on Feb. 20, 2009. The method for forming the article may optionally include one or any combination of the following: sealingly attaching a base sheet to one or more substructures such as an inner ring, an outer ring, or both; sealingly attaching a cover sheet to one or more substructures such as an inner ring, an outer ring, or both; or cutting, stamping or punching one or more indents along the outer periphery of a base sheet and/or a cover sheet.

According to the teachings herein, the capsular structure (or a segment of the capsular structure) may be formed by a process including sealingly attaching two sheets about their periphery. Preferably at least one of the sheets is embossed, stamped, or otherwise formed so that it is capable of holding a liquid. More preferably both sheets are embossed, stamped or otherwise formed. For example the capsular structure, or a segment thereof, may be formed by a process including one or more of the following steps: partially joining only a portion of an outer periphery of a first sheet to a second sheet so that a space between the two sheets can be filled with a thermal energy storage material; filling at least a portion of the space between the two sheets with a thermal energy storage material; and joining the remainder of the sheets so that a sealed space including thermal energy storage material is formed. One or more of these steps may be repeated to provide a structure including a plurality of sealed spaces.

Suitable sheets for encapsulating the thermal energy storage material include thin metal sheets (e.g., metal foil) that are durable, corrosion resistant, or both, so that the sheet is capable of containing the thermal energy storage material, preferably without leakage. The metal sheets may be capable of functioning in a vehicle environment with repeated thermal cycling for more than 1 year and preferably more than 5 years. The metal sheet may otherwise have a substantially inert outer surface that contacts the thermal energy storage material in operation. The outer surface of the metal sheet that contacts the thermal energy storage material should include or consist essentially of one or more materials that do not significantly react with, corrode, or both, when contacted with the thermal energy storage material. Without limitation, exemplary metal sheets that may be employed include metal sheets having at least one layer of brass, copper, aluminum, nickel-iron alloy, bronze, titanium, stainless steel or the like. The sheet may be a generally noble metal or it may be one that includes a metal which has an oxide layer (e.g., a native oxide layer or an oxide layer which may be formed on a surface). One exemplary metal sheet is an aluminum foil which comprises a layer of aluminum or an aluminum containing alloy (e.g. an aluminum alloy containing greater than 50 weight percent aluminum, preferably greater than 90 weight percent aluminum). Another exemplary metal sheet is stainless steel. Suitable stainless steels include austenitic stainless steel, ferritic stainless steel or martensitic stainless steel. Without limitation, the stainless steel may include chromium at a concentration greater than about 10 weight percent, preferably greater than about 13 weight percent, more preferably greater than about 15 weight percent, and most preferably greater than about 17 weight percent. The stainless steel may include carbon at a concentration less than about 0.30 weight percent, preferably less than about 0.15 weight percent, more preferably less than about 0.12 weight percent, and most preferably less than about 0.10 weight percent. For example, stainless steel 304 (SAE designation) containing 19 weight percent chromium and about 0.08 weight percent carbon. Suitable stainless steels also include molybdenum containing stainless steels such as 316 (SAE designation). The metal sheet may have any art known coating that may reduce or eliminate the corrosion of the metal sheet.

The metal sheet has a thickness sufficiently high so that holes or cracks are not formed when forming the sheet, when filling the capsules with thermal energy storage material, during use of the capsules, or any combination thereof. For applications such as transportation, the metal sheet preferably is relatively thin so that the weight of the heat storage device is not greatly increased by the metal sheet. Suitable thicknesses of the metal sheet may be greater than about 10 μm, preferably greater than about 20 μm, and more preferably greater than about 50 μm. The metal foil may have a thickness less than about 3 mm, preferably less than 1 mm, and more preferably less than 0.5 mm (e.g., less than about 0.25 mm).

FIG. 8 illustrates a cross-section of an exemplary heat storage device 80 having a plurality of articles 10″, and 10′″ each laving thermal energy storage material 26 encapsulated in a plurality of sealed spaces 14. The articles are arranged in an insulated container 82 which may have a generally cylindrical shape. The device includes an article 10″ having a first adjacent article 10′″(a) and a second adjacent article 10′″(b), The article 10″ and its first adjacent article 10′″(a) may be arranged with the top surfaces (i.e., exterior surfaces) of their respective flat cover sheets generally in contact. The article 10″ and the second adjacent article 10′″(b) may have generally mating surfaces (e.g., the exterior surfaces of their respective base sheets may be generally mating surfaces) and may be arranged so that they partially nest together. A spacer (not shown) may be used to maintain a distance between the article 10″ and its second adjacent article 10′″(b) so that a heat transfer fluid can flow through a radial flow path 83 in a generally radial direction between the two articles, 10″ and 10′″(b). The space between the article 10″ and the second adjacent article 10′″(b) is part of the heat transfer fluid compartment. As illustrated in FIG. 8, each article may have a surface (e.g., a surface of the base sheet) that is in contact with the heat transfer fluid compartment so that the heat transfer fluid can be in direct contact with each article and preferably each seated space. As illustrated in FIG. 8, each radial flow path 83 may have the same length, the same cross-section, or even may be congruent. Each article has an opening near its center. The openings are also part of the heat transfer fluid compartment. The articles 10″ and 10′″ are arranged so that their openings form a central axial flow path 84. The space between the outer periphery of the articles 10″ and 10′″ and the interior surface of the container 85 is also part of the heat transfer fluid compartment and forms an outer axial flow path 86. The heat storage device has a first orifice 87 that is in fluid connection with the central axial flow path 84. The heat storage device may have a first seal or plate 88 that separates the first orifice 87 from the outer axial flow path 86. The container 82 has a second orifice 89 which may be on the same side of the container as the first orifice 87, or on a different side of the container, as illustrated in FIG. 8. The heat storage device may have a second seal 90 that separates the second orifice 89 from the central axial flow path. The first seal, the second seal, or both may prevent a fluid from flowing between the two axial flow paths 84 and 86, without flowing through a radial flow path 83. With reference to FIG. 8, a fluid flowing between the first orifice 87 and the second orifice 89 must flow through a portion of the central axial to path 84, and through a portion of the outer axial flow path 86. The heat transfer fluid must also flow through one of the radial flow paths 83 between flowing through the two axial flow paths 84, 86. The sizes of the two axial flow paths preferably are selected so that the hydrodynamic resistance of the fluid is generally constant regardless of which radial flow path a portion of the fluid takes. As such, the flow of the heat transfer fluid through the heat storage device is preferably a Tichelmann system The container 82 preferably is insulated. For example, the container may have an inner wall 91 and an outer wall 92 and the space between the two walls 93 may be evacuated. The device may also have one or more springs, such as one or more compression springs 94, that exerts a compressive force on the stack of articles.

FIG. 9 illustrates a heat storage device 80′ having two orifices 87′ and 89′ on one side of the container. Such a device may employ as tube 95 that is connected to the first orifice 87′ for flowing the fluid between the first orifice and a region 96 of the central axial flow path 84′ furthest from the first orifice. With reference to FIG. 9, the first seal 88′ and the second seal 90′ may be employed to prevent a fluid from flowing from the first orifice 87′ to the second orifice 89′ without first flowing through a radial flow path 83. Again, by selecting the sizes fare the two axial flow paths 86 and 84′, the heat storage device 80′ of FIG. 9 may be characterized as a Tichelmann system.

Heat Storage System

The heat storage device may be used in a heat storage system that employs one or more heat transfer fluids for transferring heat into the heat storage device, for transferring heat out of the heat storage device, or both.

Heat Transfer Fluid/Working Fluid

The heat transfer fluid used to transfer heat into and/or out of the thermal energy storage material may be any liquid or gas so that the fluid flows (e.g., without solidifying) through the heat storage device and the other components (e.g., a heat providing component, one or more connecting tubes or lines, a heat removing component, or any combination thereof) through which it circulates when it is cold. The heat transfer fluid may be any art known heat transfer fluid or coolant that is capable of transferring heat at the temperatures employed in the heat storage device. The heat transfer fluid may be a liquid or a gas. Preferably, the heat transfer fluid is capable of flowing at the lowest operating temperature that it may be exposed to during use (e.g., the lowest expected ambient temperature). For example, the heat transfer fluid may be a liquid or gas at a pressure of about 1 atmosphere pressure and a temperature of about 25° C., preferably about 0° C., more preferably −20° C., and most preferably at about −40° C. Without limitation, a preferred heat transfer fluid for heating and/or cooling the one or more electrochemical cells is a liquid at about 40° C.

The heat transfer fluid should be capable of transporting a large quantity of thermal energy, typically as sensible heat. Suitable heat transfer fluids may have a specific heat (measured for example at about 25° C.) of at least about 1 J/g·K, preferably at least about 2 J/g·K, even more preferably at least about 2.5 J/g·K, and most preferably at least about 3 J/g·K. Preferably the heat transfer fluid is a liquid. For example, any art known engine coolant may be employed as the heat transfer fluid. The system preferably employ a single heat transfer fluid for transferring heat into the thermal energy storage material in the heat storage device and for removing heat from the thermal energy storage material in the heat storage device. Alternatively, the system may employ a first heat transfer fluid for transferring heat to the thermal energy storage material and a second heat transfer fluid for removing heat from the thermal energy storage material. In a system including a first heat transfer fluid and a second heat transfer fluid, the first heat transfer fluid flows through a first heat transfer fluid compartment and the second heat transfer fluid flows through a second heat transfer fluid compartment, wherein the heat transfer fluid compartments are generally separated by a relatively low thermal conductivity material, such as the thermal energy storage material. For example, at least 20%, at least 50%, or at least about 80%, of the surface area of the first heat transfer fluid compartment may contact or be surfaces of articles containing the thermal energy storage material. This contrasts with a heat exchanger in which two heat transfer fluids are in relatively good thermal communication.

Without limitation, heat transfer fluids which may be used alone or as a mixture include heat transfer fluids known to those skilled in the art and preferably includes fluids containing water, one or more alkylene glycols, one or more polyalkylene glycols, one or more oils, one or more refrigerants, one or more alcohols, one or more betaines, or any combination thereof. The heat transfer fluid may include (e.g., in addition to or in lieu of the aforementioned fluids) or consist essentially of a working fluid such as one described hereinafter. Suitable oils which may be employed include natural oils, synthetic oils, or combinations thereof. For example, the heat transfer fluid may contain or consist substantially (e.g., at least 80 percent by weight, at least 90 percent by weight, or at least 95 percent by weight) of mineral oil, caster oil, silicone oil, fluorocarbon oil, or any combination thereof.

A particularly preferred heat transfer fluid includes or consists essentially of one or more alkylene glycols. Without limitation, preferable alkylene glycols include from about 1 to about 8 alkylene oxy groups. For example the alkylene glycol may include alkylene oxy groups containing from about 1 to about 6 carbon atoms. The alkylene oxy groups in a alkylene glycol molecule may be the same or may be different. Optionally, the alkylene glycol may include a mixture of different alkylene glycols each containing different alkylene oxy groups or different ratios of alkylene oxy groups. Preferred alkylene oxy groups include ethylene oxide, propylene oxide, and butylene oxide. Optionally, the alkylene glycol may be substituted. For example the alkylene glycol may be substituted with one or two alkyl groups, such as one or two alkyl groups containing about 1 to about 6 carbon atoms. As such the alkylene glycol may include or consist essentially of one or more alkylene glycol monoalkyl ethers, one or more alkylene glycol dialkyl ethers, or combinations thereof. The all glycol may also include a polyalkylene glycol. Particularly preferred alkylene glycols include ethylene glycols, diethylene glycol, propylene glycol, and butylene glycol. Any of the above glycols may be used alone or as a mixture. For example, the glycol may be employed as a mixture with water. Particularly preferred heat transfer fluids include mixtures consisting substantially (e.g., at least 80 weight percent, at least 90 weight percent or at least 96 weight percent based on the total weight of the heat transfer fluid) or entirely of a mixture of a glycol and water. The concentration of water in the mixture preferably is greater than about 5 weight percent, more preferably greater than about 10 weight percent, even more preferably greater than about 15 weight percent, and most preferably greater than about 20 percent, based on the total weight of the heat transfer fluid. The concentration water in the mixture is preferably less than about 95 weight percent, more preferably less than about 90 weight percent, even more preferably less than about 85 weight percent, and most preferably less than about 80 weight percent. The concentration of glycol in the mixture preferably is greater than about 5 weight percent, more preferably greater than about 10 weight percent, even more preferably greater than about 15 weight percent, and most preferably greater than about 20 percent based on the total weight of the heat transfer fluid. The concentration of glycol in the mixture is preferably less than about 95 weight percent, more preferably less than about 90 weight percent, even more preferably less than about 85 weight percent, and most preferably less than about 80 weight percent.

Optionally, the heat transfer fluid may include or consist substantially entirely of a working fluid. For example, the system may include a working fluid that flows through the heat storage device where it is heated and evaporates and then to one or more components (such as a component to be heated f where the working fluid condenses, As such, the heat storage device may function as an evaporator for the working fluid and a component to be heated may function as a condenser for the working fluid. If a working fluid is employed, the heat provided to the condenser preferably includes the heat of vaporization of the working fluid. The system may include a cold line for returning the working fluid to heat storage device, and a heat line for removing working fluid from the heat storage device. The cold line and the heat line preferably are capable of containing the working fluid without leaking as it is flows through a loop. When the heat storage device (e.g., the thermal energy storage material in the heat storage device) is at a temperature sufficient to cause the combined vapor pressure of all components of the working fluid to exceed about 1 atmosphere and a valve is opened to allow the flow of the working fluid, the working fluid may be a) pumped by a capillary structure; b) at least partially vaporized; c) at least partially transported to the condenser; and d) at least partially condenses in the condenser, so that heat is removed from the heat storage device. As such the system may optionally include a capillary pumped loop.

Working Fluids

The working fluids may be any fluid that can partially or completely evaporate (transition from a liquid to a gaseous state) in the heat storage device when the thermal energy storage material is at or above its liquidus temperature. Suitable working fluids e.g., for the capillary pumped loop) include pure substances and mixtures having one or any combination of the following characteristics: a good chemical stability at the maximum thermal energy storage system temperature, a low viscosity (e.g., less than about 100 mPa·s), good wetting of the capillary structure (e.g., good wick wetting), chemical compatibility with (e.g., the working fluid causes low corrosion of) the materials of the capillary pumped loop (such as the container material, the materials employed to encapsulate the thermal energy storage material, the materials of the vapor and liquid lines, and the like), a temperature dependent vapor pressure that is conducive to both evaporator and the condenser temperatures, a high volumetric latent heat of vaporization (e.g., the product of the latent heat of fusion and the density of the working fluid at about 25° C. in units of megajoules per liter may be greater than about 4 MJ/liter), a freezing point less than or equal to the freezing point of the heat transfer fluid of the condenser (e.g., a freezing point less than or equal to the freezing point of antifreeze), or a freezing point less than or equal to about −40° C. For example, the equilibrium state of the working fluid may be at least 90 percent liquid at a temperature of −40° C. and a pressure of 1 atmosphere.

Without limitation, exemplary working fluids may include or consist essentially of one or more alcohols, one or more ketones, one or more hydrocarbons, a fluorocarbon, a hydrofluorocarbon (e.g., an art known hydrofluorocarbon refrigerant, such as an art known hydrofluorocarbon automotive refrigerant), water, ammonia, or any combination thereof.

The vapor pressure of the working fluid should be high enough in the evaporator so that a vapor stream is produced that is sufficient to pump the working fluid. Preferably, the vapor pressure of the working fluid should be high enough in the evaporator so that a vapor stream is produced that is sufficient to carry the desired thermal power measured in watts from the evaporator to the condenser. The vapor pressure of the working fluid in the evaporator preferably is sufficiently low so that the capillary pumped loop does not leak and does not rupture.

The wetting of the working fluid to the capillary structure may be characterized by a contact angle of the working fluid on the material of the capillary structure. Preferably, the contact angle is less than about 80°, more preferably less than about 70°, even more preferably less than about 60°, and most preferably less than about 55°.

The working fluid preferably condenses at moderate pressures at temperatures below about 90° C. For example, the working fluid may condense at about 90° C. at a pressure less than about 2 MPa, preferably less than about 0.8 MPa, more preferably less than about 0.3 MPa, even more preferably less than about 0.2 MPa, and most preferably less than about 0.1 MPa.

The working fluid preferably can flow at very low temperatures. For example, the working fluid may be exposed to very low ambient temperatures and preferably is capable of flowing from the condenser to the heat storage device at a temperature of about 0° C., preferably about −10° C., more preferably about −25° C., even more preferably about −40° C., and most preferably about −60° C. The working fluid preferably is in a gas state when it is at a temperature of the fully charged heat storage device. For example, the working fluid may have a boiling point at 1 atmosphere less than the phase transition temperature of the thermal energy storage material in the heat storage device, preferably at least 20° C. less than the phase transition temperature of the thermal energy storage material, and more preferably at least 40° C. less than the phase transition temperature of the thermal energy storage material. In various aspects of the invention, it may be desirable for the working fluid to have a boiling point at 1 atmosphere (or the temperature at which the combined vapor pressure of all of the components of the working fluid is equal to 1 atmosphere may be) greater than about 30° C., preferably greater than about 35° C., more preferably greater than about 50° C., even more preferably greater than about 60° C., and most preferably greater than about 70° C. (e.g., so that the working fluid is a liquid at ambient conditions). In various aspects of the invention, the boiling point at 1 atmosphere of the working fluid may be (or the temperature at which the combined vapor pressure of all of the components of the working fluid is equal to 1 atmosphere may be) less than about 180° C., preferably less than about 150° C., more preferably less than about 120° C., and most preferably less than about 95° C.

A particularly preferred working fluid includes or consists substantially of water and ammonia. For example the combined concentration of water and ammonia in the working fluid may be at least about 80 weight percent, more preferably at least about 90 weight percent, and most preferably at least about 95 weight percent based on the total weight of the working fluid) water and ammonia. The concentration of ammonia may be sufficient to keep the boiling point of the working fluid below the boiling point of water (e.g., at least 10° C. below the boiling point of water). The concentration of ammonia may be greater than about 2 weight percent, preferably greater than about 10 weight percent, more preferably greater than about 15 weight percent and most preferably greater than about 18 weight percent based on the total weight of the working fluid. The concentration of ammonia may be less than about 80 weight percent, preferably Less than about 60 weight percent, more preferably less than about 40 weight percent and most preferably less than about 30 weight percent based on the total weight of the working fluid. The concentration of water in the working fluid may be greater than about 20 weight percent, preferably greater than about 40 weight percent, more preferably greater than about 60 weight percent and most preferably greater than about 70 weight percent based on the total weight of the working fluid. The concentration of water in the working fluid may be less than about 98 weight percent, preferably less than about 95 weight percent, more preferably less than about 90 weight percent, even more preferably less than about 85 weight percent, and most preferably less than about 82 weight percent based on the total weight of the working fluid. For example a solution of about 21 weight percent ammonia and about 79 weight percent water has a liquidus point of about −40° C. and the upper limit of a boiling range at 1 atmosphere of less than about 100° C. This solution may be stored (e.g., as a liquid) in a non-pressurized container at room temperature.

Preferably the working fluid has a combined vapor pressure of all of its components equal to 1 atmosphere at one temperature from about 0° C. to about 250° C.

The working fluid is capable of efficiently transferring thermal energy from the heat storage device so that the amount of working fluid needed to remove an amount of heat from the heat storage device is relatively small (e.g., compared to a device that uses a heat transfer fluid that is not a working fluid to remove the heat). Preferably a large portion of the heat transferred by the working fluid is transferred in the form of heat vaporization. The volume of working fluid, the flow rate of the working fluid, or both, may be relatively low in the thermal energy storage compared to a system that employs a heat transfer fluid that is not a working fluid and has the same initial power. The flow rate of the working fluid the working fluid in the liquid state flowing into the heat storage device) per liter of the container of the heat storage device may be less than about 5 liters/min, preferably less than about 2 liters/min, more preferably less than about 1 liter/min, even more preferably less than about 0.5 liters/min, and most preferably less than about 0.1 liters/ min. The ratio of the volume of the working fluid in the system to the total volume in the container of the heat storage device, or to the volume of the thermal energy storage material in the heat storage device should be sufficiently low so that the total weight of the system is not excessively impacted by the weight of the working fluid. The ratio of the volume of the working fluid in the system (e.g., in the capillary pumped loop) to the total volume of the container (i.e., the volume inside the container) of the heat storage device (or even the ratio of the volume of the working fluid in the system to the volume of the thermal energy storage material in the heat storage device) may be less than about 20; preferably less than 10, more preferably less than about 4, even more preferably less than about 2, and most preferably less than about 1.

As described above, the working fluid may transfer some of the thermal energy in the form of heat of heat of vaporization. The working fluid preferably has a high heat of vaporization so that the amount of heat that can be transferred is high. Suitable working fluids for the heat storage device may have a heat of vaporization greater than about 200 kJ mole, preferably greater than about 500 kJ/mole, more preferably greater than about 750 kJ/mole, even more preferably greater than about 1000 kJ/mole, and most preferably greater than about 1200 kJ/mole.

In applications where the temperature of the working fluid may be less than 0° C., the working fluid preferably is not water (e.g., so that the working fluid does not freeze, cause a rupture, or both).

It will be appreciated that the materials that contact with the working fluid may be resistant to corrosion from the working fluid. For example, any one or all of the surfaces of the heat storage device or the heat storage system that may come in contact with the working fluid (e.g., the interior of the working fluid vapor line, the interior of the working fluid liquid line, the surfaces of the heat transfer fluid compartment of the heat storage device, the interior surfaces of one or more valves, the surface of a working fluid compartment in the condenser, the interior surface of a working fluid reservoir, and the like) may be made of stainless steel.

It will be appreciated that any of the working fluids or heat transfer fluids employed in the thermal energy storage system described herein may include an additives package. Such additive packages are well known to those skilled in the art and are adapted to fit the system in which the device of the invention may be utilized. For example the additives package may include a stabilizer, a corrosion inhibitor, a lubricant, an extreme pressure additive, or any combination thereof.

Optional Heater

The heat storage system may optionally include one or more heaters. The heater may be any heater that is capable of increasing the temperature of the thermal energy storage material in the heat storage device to a temperature above its transition temperature. The heater may be any heater that converts energy (e.g., electrical energy, mechanical energy, chemical energy, or any combination thereof) into heat (i.e., thermal energy). The one or more heaters may be one or more electric heaters. The one or more heaters may be employed to heat some or all of the thermal energy storage in the heat storage device. Preferably the system includes one or more heaters that are in thermal communication with a heat storage device. For example, the system may include one or more heaters within the insulation of a heat storage device. An electric heater may employ electricity from one or more electrochemical cells, from an external source, or both. For example, when a vehicle is plugged into an outlet connected to a stationary object, the heat storage device may be maintained at a temperature above the liquidus temperature of the thermal energy storage material in the heat storage device using the electricity form an external source. When the vehicle is not plugged into an outlet connected to a stationary object, the heat storage device may be maintained at a temperature above the liquidus temperature of the thermal energy storage material in the heat storage device using electricity generated from an electrochemical cell.

The heat storage device may be used in a process for heating one or more components. The process may include flowing a heat transfer fluid through the heat transfer device. The step of flowing a heat transfer fluid through the heat storage device may include flowing a heat transfer fluid having an initial temperature through an inlet of the device; flowing the heat transfer fluid through an axial flow path so the heat transfer fluid can be divided into a plurality of radial flow paths; flowing the heat transfer fluid through a radial flow path so that it can remove heat from the thermal energy storage material, wherein the thermal energy storage material has a temperature greater than the initial temperature of the heat transfer fluid; flowing the heat transfer fluid through a different axial flow path so that a plurality of radial flow paths can recombine; flowing the heat transfer fluid having an exit temperature through an outlet of the device; or any combination thereof. Preferably the heat transfer fluid exit temperature is greater than the initial temperature of the heat transfer fluid. The process for heating one or more components may employ a flow path through the heat storage device including one of a selection of radial flow path and two axial flow paths, the flow path having a total flow length, wherein the total flow length is generally constant for the different radial flow paths.

The heat storage device and/or the heat storage system may characterized as having a relatively high power (e.g., as measured during the initial 30 or 60 seconds of heating) so that it can rapidly heat a component, such as an internal combustion engine. The heat storage device and/or the heat storage system may be characterized by an average power greater than about 5 watts, preferably greater than about 10 watts, more preferably greater than about 15 watts, and most preferably greater than about 20 watts.

The heat storage device and/or the heat storage system may be characterized as having a relatively high power density, so that it can hold a large quantity of thermal energy in a relatively small compartment. For example, the heat storage device and/or the heat storage system may be characterized as having a power density greater than about 4 kW/L, preferably greater than about 8 kW/L, more preferably greater than about 10 kW/L, and most preferably greater than about 12 kW/L.

The heat storage device and/or the heat storage system may be characterized as having a relatively low pressure drop of the heat transfer fluid (measured at a heat transfer fluid flow rate of about 10 L/ min). For example, the heat storage device and/or the heat storage system may be characterized as having a heat transfer fluid pressure drop less than about 2.0 kPa, preferably less than about 1.5 kPa, more preferably less than about 1.2 kPa, and most preferably less than about 1.0 kPa.

By way of example, the thermal energy storage system may be employed in a transportation vehicle (e.g., an automotive vehicle) for storing energy from an engine exhaust gas. When the engine produces exhaust gas, a bypass valve may either direct the flow of the gas through the heat storage device so that the heat storage device is charged, or through a bypass line to prevent the heat storage device from overheating. When the engine is shut down, e.g. during a period when the vehicle is parked, a substantial portion of the heat stored in the heat storage device may be retained for a long time (e.g., due to vacuum insulation surrounding the heat storage device). Preferably at least 50% of the thermal energy storage material in the heat storage device remains in a liquid state after the vehicle has been parked for 16 hours at an ambient temperature of about −40° C. If the vehicle is parked for a long enough time (e.g., at least two or three hours) for the engine to cool down substantially (e.g., so that the difference in temperature between the engine and the ambient is less than about 20° C.), the heat stored in the heat storage device may be discharged into the cold engine or other heat recipient indirectly by flowing a heat transfer fluid (such as the engine coolant) through the heat exchanger that includes the condenser for the working fluid. The working fluid is circulated in a capillary pumped loop using the capillary structure inside the heat storage device where the working fluid is vaporized. The heat from the working fluid is transferred to the engine coolant in the heat exchanger. By employing the heat storage device, heat that otherwise would be wasted may be captured during a previous trip to mitigate cold start and/or provide instant cockpit heating.

A thermal energy storage system for storing heat, such as heat from an vehicle exhaust may include some or all of the features illustrated in FIG. 10. The thermal energy storage system 100 includes the heat storage device 101. The thermal energy storage system may include a heat exchanger or condenser 102 having a first inlet 117 for a first heat transfer fluid 107 and a first outlet 117 for the first heat transfer fluid. The thermal energy storage system 100 may have a tube (e.g., a line) 113 connecting the first heat transfer fluid inlet 111 of the heat exchanger 102 to the first heat transfer fluid outlet of the heat storage device 101. The thermal energy storage system 100 may have a tube 109 connecting the first heat transfer fluid outlet 117 of the heat exchanger 102 to the first heat transfer fluid inlet of the heat storage device 101. The first heat transfer fluid 107 flows through a first heat transfer fluid compartment of the heat storage device 101. The first heat transfer fluid may flow through a first heat transfer fluid compartment of the heat exchanger 102. The first heat transfer fluid may be a working fluid, the line from the heat storage device 101 to the heat exchanger 102 may be a vapor line, the heat exchanger 102 may be a condenser for the working fluid, and the first heat transfer fluid compartments may be working fluid compartments. As such, the thermal energy storage system 100 may contain a capillary pumped loop including the working fluid compartment in the heat storage device, a working fluid compartment in the condenser, the working fluid vapor tube 109, and the working fluid liquid tube 113. The thermal energy storage system also includes one or more heat transfer fluid or working fluid reservoirs 110. When used in a capillary pumped loop, the reservoir 110 preferably has a fill level that is higher in elevation than the working fluid inlet of the heat storage device 101 and lower than the elevation of the working fluid outlet 117 of the condenser, the working fluid inlet 111 of the condenser, or both. The thermal energy storage system 100 may include a valve 118 to regulate the flow of the first heat transfer fluid in the tube 113 connecting the heat storage device 101 and the heat exchanger 102. For example, the valve 118 may be used to prevent the heat transfer fluid from circulating when the heat storage device is charging and when the heat storage device is storing heat. The valve 118 may be opened when it is desired to discharge heat from the heat storage device. Referring again to FIG. 10, the thermal energy storage system may includes a heat transfer fluid inlet line 108 and a heat transfer fluid outlet line 106, for flowing second heat transfer fluid into and out of the heat storage device 101. The thermal energy storage system may also have a heat transfer fluid bypass line 105 and a diverter valve (e.g., a bypass valve) 104 to divert some or all of the second heat transfer fluid to the bypass line 105 (e.g., when the heat storage device is fully charged, or when the temperature of the second heat transfer fluid is below a temperature of the thermal energy storage material in the heat storage device 101). The thermal energy storage system may also include a cold line 116 for providing another heat transfer fluid into the heat exchanger, and a heat line 116 for removing the heated heat transfer fluid from the heat exchanger 102. The cold line 116 and heat line 115 are part of a heat transfer fluid loop 114. The heat transfer fluid loop 114 may contains an engine coolant. The heat transfer fluid loop 114 may be connected to an internal combustion engine 103. As such, the thermal energy storage system 100, may heat an internal combustion engine 103 with the energy stored in the heat storage device 101.

The transfer of heat using the working fluid may begin by opening the working fluid valve (i.e., the discharge valve). The sealed working fluid reservoir connected to the loop via an additional liquid line serves to accommodate changes in the working fluid liquid volume inside the loop without substantial pressure changes. Once sufficient or all useful heat is transferred from the heat storage device, the discharge valve may close. The remaining working fluid in the heat storage device may evaporate (e.g., from heat remaining in the heat storage device or when the heat storage device begins to charge) and then condenses in the condenser. As the heat storage device becomes evacuated of the working fluid, the liquid level of the working fluid level may change (e.g., rise).

The heat storage device may optionally be a cross-flow heat exchanger (i.e., having a flow direction for the working fluid and a perpendicular flow direction for the flow of the exhaust gas). For example, during operation, the heat storage device may include three chambers occupied by 1) exhaust gas; 2) stagnant phase change material (e.g., inside capsules, such as a blisters pack); and 3) working fluid. All three chambers are kept separate by thin walls made of an appropriate material, preferably stainless steel. Exhaust gas may flow between the surfaces (e.g., the curved surfaces) of the capsules of phase change material inside blisters, and the working fluid may flow between different surfaces (e.g., flat surfaces) of the capsules of phase change material inside blisters in a direction that is generally perpendicular to the exhaust gas flow direction. The liquid working fluid entering its chamber preferably wets a capillary structure (e.g., a metal wick) and gets transported up against the combined forces of gravity and vapor pressure by the capillary forces acting upon the working fluid liquid menisci formed inside the capillaries. This flow is sustained by continuous evaporation of the liquid using the heat drawn from the phase change material inside blisters. The vapor of working fluid leaves the capillary structure and escapes to the top of the device via vapor channels which may be interdigitated between columns of the capillary structure squeezed between the surfaces (e.g., the flat surfaces) of the capsules of phase change material inside blisters. The vapor of working fluid flows into the condenser where it transfers its heat of vaporization and sensible heat to the cold coolant and becomes liquid again to return to the heat storage device and continue its circulation in the loop, being pumped only by the capillary forces existing inside the capillary structure (e.g., metal wick) that is partially impregnated by liquid working fluid. All columns of the capillary structure may be connected to a common porous base. Such a porous base may be employed to distribute the liquid working fluid entering from the bottom of the device to the different columns.

Furthermore, the present invention may be used in combination with additional elements/components/steps. For example, absorption or adsorption cycle refrigeration system for air conditioning may be used as the heat recipient instead of or in addition to the cold coolant (e.g., the condenser may serve also as an evaporator for the refrigerant circulating inside an air conditioner's fluid loop). In another application, a steady-state waste heat recovery system using a heat engine, e.g. a Rankine cycle, can be constructed so that it uses the same or different capillary pumped loop working fluid and adds a mechanical power generating turbine to the vapor line between the heat storage device and the condenser, (e.g., to overcome high vapor pressure upstream from the turbine), and/or adds a liquid pump to the liquid line between the condenser and heat storage device. The above turbine can convert a part of the captured from the exhaust gas waste heat into useful mechanical or electrical work and thus improve the overall fuel efficiency of the vehicle.

While the present invention may be susceptible to various modifications and alternative forms, the exemplary embodiments discussed above have been shown by way of example. However, it should again be understood that the invention is not intended to be limited to the particular embodiments disclosed herein. Indeed, the present techniques of the invention are to cover all modifications, equivalents, and alternative falling within the spirit and scope of the invention as defined by the following appended claims. 

1. An article comprising a capsular structure having one or more sealed spaces wherein the sealed spaces encapsulate one or more thermal energy storage materials; wherein the capsular structure has one or more fluid passages which are sufficiently large to allow a heat transfer fluid to flow through the one or more fluid passages, and when a heat transfer fluid contacts the capsular structure the thermal energy storage material is isolated from the heat transfer fluid.
 2. The article of claim 1, wherein the capsular structure includes two sheets capable of encapsulating the thermal energy storage material, the sheets having an outer periphery and each sheet being sealingly attached at least along the outer periphery to each other and/or to one or more additional sub-structures and forming the one or more sealed spaces therebetween containing the thermal energy storage materials.
 3. The article of claim 2, wherein the sheets are sealingly attached to each other along the outer periphery and along the periphery of its opening.
 4. The article of claim 1, wherein the capsular structure has a top surface and an outer periphery; wherein the top surface includes two or more grooves each extending from the fluid passage to the outer periphery and each providing fluid connection between the passage and the outer periphery.
 5. The article of claim 1, wherein the capsular structure has a first outer surface and a second outer surface, the capsular structure has a thickness defined by the average separation between the first outer surface and the second outer surface; wherein the capsular structure is sufficiently thin so that heat can be quickly transferred out of the one or more sealed spaces; the thermal energy storage material is a phase change material having a solid to liquid transition temperature greater than about 30° C. and less than about 350° C.; and the one or more sealed spaces have a total interior volume, at a temperature of about 25° C., and the sealed spaces contains a total volume of thermal energy storage material, at a temperature of about 25° C., wherein the ratio of the total volume of thermal energy storage material to the total interior volume is at least about 0.50; so that the article can store a large amount of thermal energy.
 6. The article of claim 5, wherein the fluid passage is near the geometric center of the first outer surface.
 7. The article of claim 1, wherein the article includes 3 or more sealed spaces.
 8. The article of claim 1, wherein the outer periphery of the article includes one or more indents, so that when a stack of the articles are placed in a hollow cylinder a heat transfer fluid can flow through the space formed by the indents; the thickness of the article is less than about 1 cm, the article has a dimension greater than about 5 cm; and a surface of the article includes one or more protrusions so that when a plurality of the articles are stacked there will be a space between the articles for the flow of a heat transfer fluid. 9-26. (canceled) 